Additional Spacers for longer length of pull on Magpul PRS?

[lengthofpull]

I am looking to add some additional LOP to my Magpul PRS. I already have the 0.80" extended butt pad. I need to add 1"-2" inches onto it. I need to add the extra length to the rear (instead of behind the receiver) to keep the cheekpiece in the proper spot. Anyone know if someone makes spacers for the PRS?

Thanks,
-LOP