Had another look and this may not be feasible. Uploading the files is doable if you know what to upload them as. The problem is that travis builds do not appear to know if they are triggered as the result of a pull request so we don't know what to upload the file as and where to post the link.
Alternate option: implement https://github.com/travis-ci/travis-ci/issues/532 so that we don't have to do this in such a hacky way.
Alternate option: implement https://github.com/travis-ci/travis-ci/issues/532 so that we don't have to do this in such a hacky way.