There are several things you will need to address.
First, you need to get a handle on the nausea. Is it just because of the feedings going in, is it because they are going in at a rate faster than he can handle? Or is there some other cause for the vomiting?
Second, get yourself a bag with a long tube attached, and don't be squeamish. If an enema bag (new, of course) works, USE IT!
Third, if you can't get a bag or something like it, use the turkey baster, take off the top bulb and SLOWLY pur a mixture of tube feeding and water in, use about a third of a can of feeding to a third of a cup of water, and see if that stays down.
Make sure his entire GI tract is functioning, and that means, don't let him get constipated or get diarrhea, either one is devastating to him at this juncture.
Good luck, keep us posted on how things are going.

Andrea