Only allow CdG on NPCs. Then, only allow it in non-combat situations: sneaking in to slit throats, executioner and the chopping block, etc.
Just house-rule it so if they actually succeed at getting to the target in such a non-combat situation, they automatically succeed.
Once initiative is rolled, no CdG allowed.
Bottom line: CdG against PC is teh sux. CdG against NPCs should be used when appropriate for the atmosphere. Otherwise, handle it with basic combat rules.
Don't be afraid the house-rule the heck out of things!