Currently got the same problem on a Merckx MXL that I'm restoring. Attached is a photo (frustratingly, because I've got less than 10 posts I'm not able to post a photo).

Given that the bolt is rounded and effectively useless, I figure drilling out as the OP did would probably be the best solution.

Just wanted to inform the community to build some testimony for this method. Will let you know how it goes.