In reply to Chip Bennett.

Chip, you make a good point. There really isn't a *good* way to offer code to a plugin developer who has their plugin in the repository. However, asking for update credentials to the repository is very much a *bad* way to offer help to a plugin developer. Even if it's a legit offer, it looks very, very suspicious.

And, I think you make a very convincing argument for using GitHub instead. In fact, just the other day, I stumbled across a plugin meant to help you update plugins hosted via GitHub. Naturally, it was on GitHub! https://github.com/jkudish/WordPress-GitHub-Plugin-Updater
Any thoughts on that plugin?