Depending on how much blur you want, around 1/15 / 1/8 with rear curtain
sync then merge in photoshop.

To do it in one exposure, you should have a perfect black background
with few wrinkles and avoid lighting it with ambient (set the ambient
lights high to illuminate the subject, but not the BG.  And then strobe
flash at whatever rate works (some flashes have a strobe that can be
interval set and for n-many shots).

If you have a digital SLR to experiment with, you'll close on a solution
quicker than with film.

Have fun.

Yes.

long