Bacon fed knave -- love it!
Just be sure to hand the card directly to the bride or the groom, or if they have a special box for them, slip it in there. Don't hand it to another family member on their behalf. Just in case.
Does the HC have time to deal with this in the middle of the celebrations? When I brought a card with cash in it, I kept it with me and then ascertained who the trusted gift collector was (MOB was not to be trusted, apparently! so the bit about not to any old relative is TRUE!) and gave it to that person at the end of the reception as they were moving the gifts to the more secure car which would transport them home.
If there's clearly a trusted gift collector, fine.
But in general, don't just hand it off to anyone and dump the responsibility on them.
In situations in which B&Gs are aware that people will give them cash, they often create some way to deal with it. And it's always better to have them accumulating ALL the cards, instead of the FOB or FOG (trustworthy though they may be) having the chore of holding on to it, passing it off, etc.
They're at the party, too!