I got same problem. The gas springs don't quite hold the weight of the bonnet.
I thought about cutting a slot in a piece of pipe and then using to lock the strut.
Someone on this site has beaten me to it.
http://www.jaguarforums.com/forum/xj...t-lock-116621/
Better than carrying a broom handle in car. (ah ! could call it a "vrooom handle")
Dave aka lots of other names