No, as of yet there is no way - and yes it will appear narrower at 720p than 480p. As it is, I don't see much point at the moment for 720p other than people who ABSOLUTELY need it output at that resolution because their telly/monitor prefers that kind of output as opposed to 480p.
You could try by taking a long hard look at the functions rom_menu and debugOutStr in cell.cpp, but I doubt whether you should even bother - I'm going to replace all this stuff eventually - and sooner rather than later.
It won't be an issue for much longer. In the meantime, the font size is tolerable at 480p mode.