OK, how do I go about uplinking a WRT54G (second router) and a WRT54GS
(main router)?

The setup I have currently at my home is a BEFSR41 (wired router)
connected to WRT54G (wireless) using the uplink port on the BEFSR41 to
a regular LAN port on the WRT54G...but the WRT54G does not have an
uplink port, so that same setup won't work here.

I do not want to create two subnets...I know how to cascade them if I
set it up that way, but I would like to avoid that if all possible.