The police won't show up, but as you've found, using the same LiveID simply associates the 4th through 7th PCs to the same subscription. You'll need to uninstall and reinstall on PCs 4 through 7 and use a *different* LiveID for each of two additional subscriptions. When you activate with a different LiveID you will be prompted for payment of a retail key.
The current limitation is one subscription for 3 PCs per LiveID, so for 7 licenses, you need 3 LiveIDs with 1 subscription each.
-steve