Richy, It sounds like you're looking for a way to keep the customers serviced rather than questioning how to earn the cash. If that's so, why not stretch the round to five weeks? You'll be able to keep it going at a sensible number of cleans per week, your customers are unlikely to complain and, if and when you take someone on, you can revert to four weekly and not lose any of your income from taking the new guy on (that does work if you give it some thought).
Vin