Well I know a purple of tricks, one issue you may face is in order to get insurance you'll need a title, in PA that's how it works at least, then you'll need to get an inspection possibly as well, in PA a moped needs only a single inspection, it stays inspected for the rest of forever when it's been done.
So as far as titles go, you'll need to apply for one at a notary, to get that you'll end up needing something along the lines of a certificate of origin, which is what the majority of small bikes and mopeds come with. Getting one isn't easy unless you know what to do, that's one of the tricks I mentioned.
Now the hardest part is inspection, if needed, in PA it needs to go to a specialist who inspects mopeds, that means that everything that a moped needs, lamps, turn signals, mirrors, brake lights, battery, all need to be dot approved items, unless you can find a super lax inspector. Now since the inspection is a life of the bike deal you should be willing to spend the extra money to get it, once it's done being inspected you can take everything off again and set it up like you like. I just get parts from the graveyard, stick them on the bike to meet the guidelines, and take them off after. It's gotten to the point where it's just a bunch of wire connectors and bolt-ons.
Get the inspection, which requires having a title, at least in PA, then you're right as rain, you can go and talk to an agent and get it insured as a small cc moped, recieve a plate, and put it on the back of the bike, anyone pulls you over and you'll get to enjoy that look of utter confusion and disbelief on the officers face when you hand him your license, registration, and proof of insurance for the motorized huffy bicycle he thought he was going to give you a hard time for.
