So work with the pizza place to get a special 95% discount then hand them cash "not related to the order". For something that's obviously a good faith contribution everyone involved will err toward the side of rubber stamping it as ok.
The rules are just a rule of thumb that we can apply evenly at scale to avoid corruption. When there's legitimately no corruption happening the rules get more flexible. If it ever becomes an issue HR will frown (because rules) but legal will apply the duck test and conclude that ~$10 pizza/person paid for by someone who doesn't need/want/isn't in a position to benefit from preferential treatment is not corruption.
