You can't prevent installation. You could put a check at app initialization that causes the app to exit immediately, by checking something like the MaxUnsignedApp registry value, but reading the registry isn't officially supported so a Store app doing it would probably be blocked.
It's a pretty pointless thing to check for anyhow; anybody who wants to could decompile the app, figure out the check, and work around it (for example, by temporarily dropping interop-unlock when the app starts). Jailbreak detection is, and always has been, a lost cause and a waste of effort.
Win8/Windows RT projects:
List of desktop apps for hacked RT devices
Native Access WebServer and Libraries
WP8 Interop Unlocks
Storage Cleanup tool
XapHandler, Root Webserver, OEM Marketplace XAPs, Bookmarklets collection (Find On Page), Interop-unlock hacks.
Do not private message me with questions that should have been posted on the forum!
Not only are you wasting your time - I'm not going to bother writing an answer to such a question for only one person - but I will probably block you from PMing me in the future as well.