Mike,

Before you re-invent the wheel and turn your G5RV into a loop,  one 
trick you can try is to change the length of the coax feed line.  It 
helps to have a few jumpers of different lengths and barrel connectors. 
   Add/remove jumpers in different combinations and you  should see some 
change in the swr on  the bands.   The trick is to find the length  that 
will let you tune a formerly untunable band, while not  making some 
other band untunable.

73, Steve KW3A