If I have a fuel return regulator and I can not return it back to my tank were is the next best place for it?

MerCruiser takes it back to the fuel filter assembly/adapter.

How about the fuel filler hose? If you can get to it, you can T the return into it.

Did you mean fuel "vent" hose? Install a "Y" fitting and good to go.

No, he means the filler hose 1&1/4 in hose, go into CP performance and find the fittings you need, I got 2 of them 2 years ago.

that's the way they rigged my Fountain when they put the 500efi's in it,

I've always returned back into fuel filter housing provided it has another in port.

It is just a bad idea to return to the filter. If you have a small pump on a relatively low hp engine, you can get away with it. As soon as you step up in power and fuel pump, you are asking for trouble. Not only will it heat up the fuel (even with a cooler), but it will continuously aerate the fuel. I will only set one up with a return to the tank. If you can get to the tank at all, then give me a call and I can give you a trick to make a return in the tank. The tank fill hose is another good option. Definitely do not use the vent hose.
Eddie