What an awful situation to have to deal with! You've done well by your little guy, poor thing.
Just wanted to pop in my 2c on getting meds into rats - I've found that if you try something on them once and they don't like it, they remain very, very, VERY sensitive to small traces of that taste or smell for about two weeks to a month afterward (on average? my experience anyway). This is a very good survival mechanism for wild rats - they become sensitised to smells and tastes that might be poisonous to them, and thus they can avoid eating these things. Not so great for us, though!
The best ways I've found to get around this are:
1.) strong-tasting/smelling concealer foods - think smoked oysters, peanut butter (diluted with something so it's not too sticky), maybe a dip (there's a red rock deli kind that's pumpkin and cashew or something that worked for me once), etc. Savoury can work better than sweet, but not always.
2.) massive dilution factor. By this I mean you put the tiny amount of medication into such a large amount of "carrier" that it's more difficult for the rat to sense. I use baby food for this, and it has usually worked very well. And even though it's not the healthiest thing, you're only giving medication short-term, so it won't hurt him if you have to give him a spoonful of baby food every day for a bit (as long as it's not the "dessert" baby food like custard - I try to pick all-fruit or all-vegetable varieties. Currently using Rafferty's Garden chunky pasta rissoni?/macaroni and cheese with vegetables).
Good luck! Hope he continues healing and stays happy, sounds like it's going well so far (med administration issues aside). And as a side note, not QUITE everyone's on the other side of the world... I'm in Aus too, but more toward Sydney way.