If you find the answer Tom - for God's sake tell me! I have the same problem.
Currently my husband has to put them in between my buttocks and waist, though it does mean I can't reach and wouldn't know if they were full of blood or anything, or disconnect to change the cannulas or take a shower etc without him. Room for two each side so that's 8 days (have to change every 2 days because of the sites breaking down) then I have found a small area on my ribs under my bra underwires (you won't have them I shouldn't think LOL - but you should be able to picture where I mean, I should have thought!) so that's 12 days, and have you actually tried the front, very slightly INNER thighs? room for another 2 on each leg on me (and I'm quite little) I have found - previously I have only used (and wrecked!) front and outer thighs. Total 20 days, so almost 3 weeks before we start at the beginning again. Hopefully that will keep me going for a bit, but if anything happens to Pete, I shall be stuck. Hopefully - nothing will but anything could happen and I HATE not being able to do it myself.
Still think how much worse it would be having to find 5 sites every day on MDI, instead of one every 2 days!