If my boat does not have a return fuel line can I come out of the fuel regulator return and run back to the fuel water separator which is before the fuel pump.

Yes you can. Mercury has done it that way

Merc does it that way, but it can create vapor lock issues.

I think they make a tee that goes in the fuel fill hose. I would set up a return it will have less air bound issues.

They do make a T for that, and it would be a better way to go. But if you can't get to your fuel fill lines, then don't be afraid to go the water sep.

These:
http://www.cpperformance.com/c-500-f...s-returns.aspx

bandaide...the deal above or a diesel sending unit which has a return line fitting are the best