I see no reason why it couldn't be done (disclaimer: I've not tried it). The way the "Sign In With XXX" functionality is kicked off is with a form submission, so at very least you should be able to...
- Use each platform's respective JS API to determine if the user already has a Twitter/Facebook session in play.
- There'll be a browser redirect, but in the end the user can be returned to the front page.
There are likely other ways to do this (maybe even ways that avoid the browser redirects), but it will take some experimentation to find them. I encourage you to try out the approach I spelled out above and let us know if it works. Or if you find a better way, we'd also be interested in hearing that.
Spring Social Project Lead