I used to press velvet on a nail board -- or a real fluffy towel. The only thing worse than pressing velvet is washing it (what a mess). What I would probably do in this case is see if I could use 505 to spray baste the velvet to a light weight interfacing (spray the interfacing not the velvet). I seem to remember there are several kinds of velvet -- some are synthetic, some are cotton. There was a gal who used to be on some of the craft shows who would iron acetate velvet on stamps -- the result is pretty impressive because the velvet is flattened only where the high parts of the stamp touch the velvet.