You can still work and claim SEISS, and I doubt it covers many £350 days.
To answer the question, be very careful not to annoy what sounds like a very lucrative client. By my maths you could actually make more money with this arrangement. 7 hours at 30 mins is 14 tests. With careful triage you could be seeing close to 100% of patients who need dispensing. Total achievable rate £430.
If you still decide to decline, PM me the details and I’ll do it.