You don't have to change anything. Just change the format of payment from fixed per ad to sweepstakes to be drawn per hourly or half hourly or quarter hourly as per admin decision. The more ad you click the more the chances of winning. Name the seeing of ads as Free to View Ads. FTV and not PTC.
Clixgrid can also be converted to sweepstakes format Clixstakes as above wherein more the clicks more the chance to win.
Paypal will not have any issues paying out Sweepstakes prizes.
This way we can preserve the integrity of
by just making slight changes according to changing times