What are you trying to gain by doing this? The upper still will not hinge forward like an AR does.
They do offer a modification to drill the lower for the detent and spring so a regular rear TD pin can be used, but they are quick to stste it is a waste of $150.00 plus the cost of whatever pin you want to use as the different pin serves no use over what come factory.
Trust me their design works just fine as it is. Drilling out the factory installed rear pin after you get the lower could cause you waaaaay more grief that you think. IF you have a fully equipped machine shop and were to make a fixture it could be done, but again to what benefit?