Why not just use the straw as a mandrel to get the Kevlar through the plug, then slide the plug off the straw onto some dries-flexible glue like E6000 once it's in its final position? Would work well for thicker Kevlar. For 100-lb, you can probably just use a heavy sewing needle to pull it through the plug.
Many good ways to skin a cat.
As opposed to a cord to rocket or cord to nose cone attachment, both of which are subject to forces potentially multiple times the weight of the rocket, there isn’t much force pushing the foam plug forward or back along the cord. About the only glue I know you should NOT use is CA, as it makes Kevlar brittle.
I’ve used the straw technique and wood or even white glue without problems. It’s not “hell for stout”, certainly not the optimal recommended adherence agent for Kevlar, foam, and plastic, but for this purpose “good enough” is indeed “good enough.”
I do think the straw adds something, the bare cord I think even glued may have a tendency to “zipper” bare foam.
In both biology and mechanics, often “surface area” is a key factor. The greater the surface area of adhesion, the better the bond.