Doc, you answerd your own question. Filler is porus and it does absorb the primer. Best bet after using filler is to use a sealer and not a primer first. Filler will absorb anything from your primer and paint to oils and aeresol sprays, so its always a good idea to seal it after its cured to keep all the nasties out. Sealer will stop that problem of absorbtion. I usually never come in this forum so you almost got no answer.
Alan, of course you can. You can do anything you can dream up. If you really want to do it I can help you out and tell you how step by step. Let me know.