Just how much steerer are we talking about that is uncut, above the headtube anyways? There is a max allowable steerer height typically 40-50mm worth of spacers + stem. The starnuts take a standard M6 bolt, usually with a low profile head and a regular head is just as acceptable.

As for holding the fork you can put the fun between your legs and hammer it in, while holding the fork with your hand as well.