I would start with the other end of gases and maeby be able to condence R1150/R23/R508 properly first ;) With 3 stages it wouldnt be that hard, but balancing everything would be a PITA. I was thinking something in the line of R134a-R410a and then one of those gases... Maeby use TEVs for all the stages and EPRs too...Too damn expensive :D
