Tony,
Using GitHub to counteract Travis-CI limitations and vice versa does seem like a dead end and could have other technical issues. But many people use Travis-CI to send data or deploy to a remote server. You wouldn't necessarily have to deploy to GitHub(The only reason we do is because our website is hosted on GitHub pages and it will be braindead easy to link to the .zip buttons for dev builds and our scenario is much different than the one MXE faces). I think using S3 for caching is any better an idea than using GitHub. They are both sub-optimal workarounds.
The enemy here is time, so Travis-CI just needs to figure out what to send and where to send it as quick as possible. In fact, Travis-CI probably just needs to signal the remote server to tell it to clone your GitHub repo and do the build and once the build is complete, notify developers via email/mailing list/etc... Digital Ocean (
https://www.digitalocean.com ) has cheap VPS hosting that could be used for this purpose.
Another option would be to contact Travis-CI people directly and explain the situation and point them to the Issues and the discussions on the mailing list. Since they provide the service for open source projects, they may make an exception to the time limit. Maybe not.
Another option could be to ask Ryan Gordon about this. I previously was considering BuildBot and later discovered Travis-CI. Ryan is familiar with BuildBot and if hosting the MXE CI system is a problem, it may be possible that he'll set you up with an account on
icculus.org considering the nature of the project. I copied him on this email in case he wishes to chime in on the matter.
Cheers,
Jonathan