Is there a spacer that you can use to increase the height of a railed gas block to the level of the rail?  I want to mount either a PRI or Troy sight on the front, but all of their versions (without an integral gas block in the case of the PRI) are rail mounted.

I want to put the front sight as far front as possible and my rail does not extend beyond the gas block.  I have considered the flip up front sights w/ gas block, but I am not sure how difficult this is so I am hesitant to mess around with it.

Thanks.