Sandbox Mode on PBE

The purpose of the PBE is to test new things that will roll out onto the live servers. What I do not get is why is there is not a mode to where you can test out different item combinations on different champions without having to wait full games to get the gold/ items. This would be a good idea to put as a custom game type for testers that want to test some late game items/ combos without having to wait 30 minutes to do so.