Are you having problems getting the last few inches of adustments, getting a good group or just getting the Aimpoint on target?
A low cost way to get a rough setup is to place the upper with out the bolt on sand bags at the range (or out the window at home), then looking through the bore at a high contrast target adjust the Aimpoint to be on that target at 25 to 50 yards.
I have had good luck with my Aimpoint on standard black targets (use the six bull targets for muzzle loaders as ends up I shoot flint locks and NFA ... leaving the rest home [:)]
At the range fire a group of three rounds, then place the rifle on the rest with sand bags front and rear, aim at the target again, then with out moving the rifle adjust the Aimpoint to the center of your three round group. You should now be sighted in, or at least close enought to adjust the last little bit using the calibration on the horz and vert adjustments (I always adjust only half the distance at the end).
Best to do the sighting in with a cool clean dry barrel that you have already fired a couple rounds to take care of any fire round fliers)
--- Early posting on "found" targets ----
At 50 yards a 4 MOA Aimpoint dot should cover a 2 inch diameter circle (if had more than 2 hours sleep in last two days would have the M16 out now to check ;-).
Assume would be nice to have the target a little larger than this and a high contrast with the background color you could:
Use a black target of 3 inch or less bulls eye
Print a black 2.5 to 3 inch circle.
Use half of a 3 by 5 note card (white on dark works also)
Cut cirle out using something round (coke can top is 2 inch dia and Bushes Beans is 3 1/4 inch).
If you do not live in Michigan use the end of the Coke can (cost a dime in Michigan for the can deposit so best to buy targets).
Regards
John