While it's not traditional, you definitely can. The easiest way to fill a vegan beignets is to use the end of a chopstick or a small metal funnel tip. Move it around to make a hole to fill. You just need to do this at the edge as the inside of a beignet is already hollow  Then use a piping tip with piping bag to fill the beignets.  Pull out as you fill until it’s no longer inserted.  If you don't have a piping bag, you could tip a small tip off a zipped sandwich bag and try your best to get it directly into the hole but this won't be as easy.