Unless you have something capable of both accurately measuring a dosage that small and stiff enough to inject, I wouldn't try anything on your own. Those are awfully small quantities, so you might see if it's safe to dilute the antibiotic with saline solution or some form of sterile water. I'd be surprised if the vet didn't have a micropipette on hand to perform the dilution for you. I'd dilute it as little as possible, but not so little that you uncomfortable with the accuracy of your dosing. One part in 10 would give you dosages from 0.2cc to 0.4cc, which should be pretty easy to do if you have steady hands.

Once diluted, it's as simple as grabbing some small syringes (1cc should be fine, unless you dilute it a lot more) and injecting the bugs. I made my inject near the back and tried to go as deep as possible through the maggot. It sounds terrible, and frankly, it is, but injecting the antibiotic as far as you can from the injection site helps ensure the highest retention of the drug as possible. Going shallow and having half of it ooze out rather defeats the point, and I'd be really scared of accidentally over medicating to compensate. Everything has side effects.

That said, obviously run all this past your vet first, and make sure to ask him to double check if the drug can safely be diluted. I'm not a medical professional, so please take everything I've said with a grain of salt.