Personally I’d either write my own plugin with a if plugin x exists clause or just edit it and send the code off to the developer saying “I have added a feature to your plugin, hope you like it” kinda deal.
Realistically though, in my own site I just edit the code and be done with it cause I know that plugin will be there cause I put it there and won’t remove it. If he is too busy to respond to feature requests he is probably too busy to update his plugin so that shouldn’t be a problem, just be sure to remember that next time he does update though.