In reply to TomGB:
I have done this many times with an assortment of different makes: the Grivel slots are very tight. However, never had that much of an issue.
Try pushing a corner through with a knife, and a small pair of pliers to complete the job, or [easier?] melt the end of the strap, pulling a long, thin, semi-solid section with your fingers [care!]
I use Grivel straps for most of my crampons are no other make is so easy to tighten/adjust/slacked wearing gloves. Petzl is the worst: nice nylon strap, but horrible buckles!