It's going to be impossible to impose ICOs/bounties to pay in ETH, especially if they don't have the funds. This is why most ICOs pay in tokens - to reduce their costs. In a way, it's like free promotion and advertisement for them. I get the sentiment but it will be unlikely to enforce this even with forming a bounty management team. This may be the most viable option:
Who would be willing to join such campaigns with this restriction?
I think you approach this from the wrong point of view. Instead of making demands to the campaign, you should be able to
offer something. If you'd manage to get many real people with real accounts and real friends to join, you'll have something valuable for campaigns, which means you can make demands.
Which may be hard to achieve because most of those who want to join campaigns are desperate and resort to creating fake accounts and spamming just to earn extra.