Are there any Republicans that meet your limited criteria of acceptable?
I don't know how you assume I that I have a limited criteria as to who Trump picks, as it doesn't make much difference to me, but here goes:
Rubio to help him in Florida or Kasich to help him in Ohio, but I am not sure that would be enough to get him elected.
I don't think Rubio would accept anyway, from what I've been reading.
Biden, for the humor he and Trump would provide together, it would be like Abbott and Costello.