The main streets are dry enough arn't they? Drive it yourself off the side streets real slow then switch with him on deerfoot, blackfoot, 14th st. south etc.
If you want to filter the test pilots just tell him that he has to give you a deposit before he test drives. If he is really serious then he will give you a deposit. If he refuses unless he gets to drive the car tell him where to go. Just use the excuse that you are tryig to cover your ass if he does something to the car. Kinda like a security deposit.
Good Luck