The FAST LSXRT I purchased from a member had already been tapped for the fuel rail mount style valve and my set-up was using the intake mounted style.
Instead of trying to plug the hole, we used an in-line style valve.
We connected the hose/line that would have attached to my valve to the nipple already installed on the intake.
We then cut the hose/line and installed an in-line style valve off of a Saturn that was in the shop that had the same connecting plug.
It pulls a little snug on the TPS plug but seems fine.
Probably why Dorman's optional in-line valve comes with what appears to be a plug extension.

Dorman Products - 911-019

Swapping from the original style to the in-line style looks SO much better than having that valve sitting right on top of the intake...especially with the LSXRT.
I guess we'll see if there are any issues with doing this when we fire her up later this week.

 

Very interesting considering I'm goin to have the same problem since I two just bought a fast LSXRT off a member and his truck has the purge valve mounted on the fuel rail and I have the one on the manifold hope it works