I'm guessing by no access to crank bolt you mean no way to physically get on it due to something in the way, not that you simply dont have one.
Is there anything else belt driven off the front you could turn? I use the alternator to turn every truck over but since you don't have one maybe you have something else?
I think something in the starter hole would be a royal PITA. Unless you run a huge extension up front.
I have not seen one specific for the duramax but haven't looked either. If the teeth on a different one match the flywheel then you could machine something to hold the tool in the starter hole.
If the teeth on the cummins one work you could machine a plate to position the tool on the flywheel and that will bolt into starter holes.
http://www.otctools.com/products/cummins-engine-barring-tool