> I have looked at using a MOSFET in this application, but I just run into a
brick
> wall when it comes to generating a gate voltage for the FET that will
always be
> positive relative to the source.

FET sounds a good way to go to me.

1.    "Photo MOS relays" provide drive to their internal FETs via light
drive. No power needed. Getting common.

    One example        http://www.aromat.com/photomos/SOP4_LowCxR.pdf
    Many available


2.    Standard opto driving FET in a bridge for AC operation.

3.    Transformer drive?

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.