I don't know if this is your arena but I'm looking to hack the T1i with magic lantern, as it appears it would solve a lot of the issues with exposure time, and maybe even the cropping. I'm just looking into it now to get the full rundown.
Also I just struck a deal for the camera for $150. It was used by this persons wife, and was hardly used at all. So it's like new with filters, bag, cables, software, battery & charger, as well as sd card. How is that for a deal.
Well I'll say good luck !! Hope your experiment works out the way you want it to . For the type images your doing nothing in astronomy here can help you . Yes you can use the stacking software but as Mal said the turbulence from heat what you call a mirage will be false evidence unless you can see the image well enough to already see a bullet hole through a 6" scope at 600 yds . Not only does your scope have great optics but your eye-sight is pretty darn good . Good luck !