This comes up every year. I would suggest having two rules rule in your constitution that say, to the effect :
1. "Any player claimed from waivers and dropped before the start of the weeks' games is not subject to the 24 hour waiver hold (or whatever your hold period is) process." This prevents someone from adding 100% of the kickers and immediately dropping them for the sole purpose of making someone take a zero one week.
2. "Your roster must be legal at all times". This means that if you don't have room to pick up that RB as a block, you can't do it. (You have to drop one of your own players in the process - is it worth it?)
If you're in a friendly league, then honoring the spirit of the rules and competition is more important than the letter of the law. If it's a no-holds-barred money league, then I'm surprised you haven't locked this down yet.