Dremel tool + deep well socket and 80 grit sand paper followed by 120 or 200 grit if you want to sand the channel. Go SLOW with the Dremel and try not to hit the base stock material.
I own 2 of these stocks. They do not have aluminum under the whole action, ONLY at the two action screw holes, i.e. the pillars. These stocks are manufactured crooked (or at least they get that way when the foam cools in the mfg process since there is no internal support, which is my theory) and they all need to be tweaked for proper bedding. The B&C stocks with full aluminum bedding are markedly better.
You will probably need to remove a bit of material on the right side of the recoil lug and just in front of that. There is probably interference there. You will also find that if you want to make the ejector port even (level) with the opening in the stock that you'll end up with many layers of masking tape around the barrel and you'll automatically be free floated. These stocks also "droop" in the forearm. FYI, the owner of B&C told me that the cost difference between a full aluminum bed and the "pillar bed" of the Sub-MOA stocks is relatively small, but Wby chooses the less expensive one anyway...
Let me know if you have questions.