I feel bad that this hasn't received and suggestions. I don't think there is a known way to enter new medications into the med database, short of AC directly showing you how, but that is very unlikely for various reasons. So, until a method is created of making custom meds try Short Keys
http://www.shortkeys.com/lite.htm, and if you're on v5 you can enter those injections as non-HM injections which will appear separately on the summary page..
HTH