Some misconceptions here.
First, a proxy is something altogether different. It’s another machine that connects to the internet via a different connection, forwarding traffic to/from you through that other connection. A moment’s though will show you that it won’t solve this problem – your traffic to/from the proxy will be blocked as well.
There is no “bittorrent port”, no defined port that bittorrent applications must or even should use. You have 65,536 different ports to choose from, and no ISP will block all of them. A machine with all its ports blocked is basically autistic!
Some of them do try to block “common” bittorrent ports, by misunderstanding that there aren’t any. Bram Cohen, who created bittorrent, set his client to default to a range of ports down around 6800, but there’s nothing special or important about that particular range. Contemporary bittorrent clients like BitComet don’t need more than one listen port, and it simply doesn’t matter which port that is.
This means that all you need to do is use a port your ISP isn’t blocking. If they’re serious about blocking wide ranges of ports, there are still some you’ll be able to use. The difficulty here is that those ports are commonly used for other sorts of traffic. For example, most web servers listen on port 80. This is by convention and agreement. Incoming traffic has to know which port to address, so these conventions arose to solve that problem. There are other port numbers commonly used for various types of mail, for file transfer, for network management, for secure connections, and so forth. Most of the ports from 0 to about 50,000 have SOME sort of generally recognized “other” purpose, though some of them are really obscure. There is no convention or generally recognized port for bittorrent. It doesn’t need or want one.
You can find a list of commonly used TCP ports and their purposes, on wikipedia. Most people should avoid ports below about 50,000 but that’s not a requirement and it won’t usually hurt anything if you do anyway.
If you run a web server, incoming traffic will be addressed to port 80. So if you try to use 80 for bittorrent, your winsock will tell you it can’t listen on that port – the web server has already grabbed it. You can’t have two different applications listening on a single port. (Or if bittorrent grabs 80 first, your web server will complain.)
But if you’re not running a web server, and don’t ever plan to, then there’s no harm in using 80 for bittorrent.
Do try not to use any of the email ports. Traffic on these will often trigger other people’s virus scanners, which is annoying and why some clients allow blocking of peers by thier port numbers.
Finally, there’s encryption. Enabling encryption prevents anyone from knowing for certain what the traffic contains. It’s possible to guess, or infer that it might be bittorrent traffic, but not to know for certain. Most ISP’s aren’t willing to block based on a guess. They’re barely willing to block at all unless the traffic is harming the network. If it’s not, then they’re being asked to serve as unpaid spies and enforcers for commercial interests, which they’re not wildly enthusiastic about doing.
BitComet can do a pretty good job of detecting whether encryption is needed, so you can set it to auto-detect this. Or if you’re certain about the blocking, set it to always use encryption, though this will lower the number of connections you’ll have.
A better, and more effective approach usually used by universities, is to block, not the bittorrent traffic, but the download of the .torrent filetype. In that situation, you could start bittorrent if you had the .torrent file, but you won’t be able to download it in the first place. All you can do then is obtain the .torrent in some other way.
There is one point that needs to be emphasized: the admins control the network, and their word is law. If the network belongs to some organization, and has forbidden the use of bittorrent or other P2P, then trying to evade the restriction can get you into trouble, including being fired, or expelled, or having your internet account cancelled altogether. If you’re not paying for the connection, you don’t have the option of changing providers.