The last time I was handed one of those pledge forms (for a new Kingdumb Hell we did not need), I "forgot" it at home. When I went to the next boasting session without the slip, they shoved another one in my face and expected me to fill in a big fat number in front of them. I can tell their intention was to strictly enforce that pledge, trying to get around $100 or more a week out of me so they could ease the burden on everyone else. Of course, I simply told them that I could not fill out the pledge form with the hounders watching (or it would not count).
The second slip simply found its way into the garbage, and I skipped the next boasting session.
If you want someone to blow off a boasting session, a good way would be to shove one of those pledge forms into their faces. And, if they shove a form like that in your face, I suggest not only not filling it out (except with a big fat zero), but skipping about a month's worth of boasting sessions so they cannot find you to hound you to sign away all your money.