Nice Pic you got there since Its Mine. I know Its Nice....lol
anyway if you have a table saw most blades are a 1/8" wide
so you want to make a 1/8"wide 1/8"deep slot or 1 pass on your table saw. then Just cut the Tolex down the middle and press in your piping or sometimes you will need to cut away a little more depending on which tolex you use. Levants are much thicker and you will need to make more room for the Piping. if its Elephant just a single slice thru the tolex will do .. hope this helps.