http://www.berkshirejagcomponents.co.../info_182.html
The above is an aftermarket jag shock to show how they come apart, all you will need is a spacer ring made up the same diameter as the spring and re assemble . I would hazard a guess and say that if anymore than 15mm in a spacer is needed it would need proper springs purchased instead. I cant find anywhere what the jag rears have as a spring rate for all I know it might be close.
Bob
I have just found out they are approx 200lbs which is to far short to pack or assist. best to buy some springs of the right poundage. Still a big saving over spax or protech.