That's intriguing someone's experimented with that! So....what you're saying is find a friend with 6 kids then as they'll have a massive grocery bill!
Have to admit my shops are generally over $30 by a fair bit. If a friend asked me to swipe a card through on one of my shops for them I'd do it. I wouldn't scrap over the points mainly because what you get isn't anything to write home about and I fly anyway.
The more I think about it, the more I think I would maybe leave the plastic card with a friend and carry the temporary card with me (maybe even laminate it to last longer) just in case I needed activity points!
Anyway, hope it's an option for the OP although I think if time were a big factor then doing a few clicks online buying points or something else would abate the stress because then it's done!