If the trick suggested by interrex doesn't do the trick for you, and it just might(great idea by the way!), Napa has aftermarket lift gate struts...part number BK 8196489 which run $31.49 each.

I'm sure that any auto parts chain has an equivalent part, so try your local Advance Auto, Carquest, O'Reilly, or whichever chain you normally use.

 

mine have 150000 miles and are fine and get used lots