You will have to bear with me as I ramble a little bit - this is hard to explain and be clear. I have tried explaining this idea before.
So the idea is to have an account that someone will pay £2 per month for. Now that money now gets split up into three categories
A winning contribution (say £1). This is sort of lie a lottery except (dependent on how many people have an account) the money is randomly allocated as winnings of something like £250 - £500 pounds each. So if you had 20,000 accounts you would have £20,000 that could be split into (say £250 pots) so 80 random people could wn £250 towards savings or bills. (This is done every month.)
A charity contribution (say 50p). Teaming up with a handful of charities would allow any user could then choose from a list which they would like their contributions to go to.
The remaining (in this example 50p) would go towards running costs.
The main idea is that it is a low amount so that people aren’t put off and it taps into the “lottery effect” just with less money and more chance of winning.
Obviously any numbers used in this example are ust nominal - I’m sure someone could do a proper analysis and work out the sweet spots.