I've pushed a change for a more generic dialog for a 'Run Custom' option and I changed the keybinding to Shift-F5.  Sorry for not doing that on the initial commit; I didn't fully understand the difference between what you were asking for and the minimal version I had committed.

For this change, I also added a 'Restart shell' checkbox to the dialog, more as a proof-of-concept than anything else (although I did hook it up, so it should be functional).  Is this the type of dialog you had in mind?

I made some comments on the PR as to some of the decisions I've run into so far with the design.

Thanks!