Ah... the big question and a big dilemma, for sure. To be honest - many people here don't go away, either on holiday or on business trips, but of course there are times when you want to or have to. Your best bet is probably to find a cat sitter with experience of testing blood glucose and giving injections - maybe not easy to find, in which case try asking local vets if any of their nurses do a bit of moonlighting and would help you out. Failing that, a friendly neighbour who might be prepared to step in? It's quite a responsbility though so you'd need to feel confident in their abilities.
Good luck!