AussieJester, thanks for your input.
i was thinking of something like a cross between forum member Jak Stoll's homemade fork (see attachment) and the old Sears Spaceliner forks
i'm thinking seat stays or chain stays would be plenty strong. i found a rear suspension spring from a junked thrift store kid's bmx bike (only $2.99USD!) and i'll take some more pictures when i get the mock-up further along.
thanks again for your interest!