It's tempting ... but technicall a no-no.
The panle lable lists the distribution systems that the panel is listed for - and yours won't make any reference to any single-phase system. Thus, the 'listing and labeling' violation.
Plus, of course, there's the usual doubled wires under one lug.
"But we'll be careful!" folks always say. I guess that most of the time they are. Good heavens, though ... panels are not that expensive!
