Ah I see now what you're looking to do. Thanks for the additional details.
So, I can't say that this would necessarily work for you, but when a package gets cached down, there are really only 2 files that get placed onto the Mac. 1) The package itself and 2) an xml file describing some basics about the package.
What you may want to try is to first cache these files down to one of your test Macs and then capturing these 2 (or more) files in the /Library/Application Support/JAMF/Waiting Room/ directory. I'd just package them up in an installer or even just make a copy of them to a different location before running any test policies on the Mac.
Since the policy run will delete those files after installation completes, making a backup of them should allow you to simply copy them back to the test Mac after each test policy run, which will be loads faster than having them re-cache down every time. Then just make sure to do a sudo jamf recon, just in case you have something like Smart Groups that depend on the existence of those cached files being in place.
There's nothing all that special about the caching process. Its simply copying down the installer and creating an xml file that rides along with it. The xml file has some information about it such as the package name, the package ID (as seen in Casper Admin) whether the package was specified to use FEU/FUT options, and a few other possible items.
Note that the "Waiting Room" directory is a locked location (only root can peek inside) so you'll want to use a Terminal session to make a copy of the files there.
sudo cp /Library/Application Support/JAMF/Waitiing Room/* ~/Desktop/CacheCopy/
If your package isn't a flat package you may need to throw the -R option into the above copy command.
Once you've gone though a policy that installs the cached packages, just do this to get them back in place-
sudo ~/Desktop/CacheCopy/* /Library/Application Support/JAMF/Waiting Room/; sudo jamf recon
Hopefully that helps you some.