No, you can't do what you want to do. There is no "getting around the no neutral problem." You'd have your current running directly into the ground.
Here's what you can do. The code allows for a single circuit (or multibranch circuit) to be run our to your garage. You could put all of your lights and outlets on this one circuit, since you already have two conductors and a ground. You just have to go in the main, remove the DP 30a breaker, put in a SP 15a or 20a breaker, and put one of the conductors in the neutral buss. I'm not sure why you want four circuits in the garage, two 15a and two 20a. Unless you're running some kind of shop that will have a few people working on fairly large power tools, I don't see all that power as necessary. You turn your lights on and work one tool at a time. And if that power is necessary, your feed wire isn't large enough. Whatever amperage you decide to go with in the main, 15 or 20, that's what you have to make the rest of the circuit conform to. So if you choose 15a, use 14awg to run your circuit, and 15a receptacles and switches. If you choose a 20a circuit, you need to use 12awg wire and 20a switches and receptacles.
If you need more power and/or circuits (say you might want to plug in a heater in the winter), you should run a new feed. Run a 10-3 for a 30a feed, or an 8-3 for a 40a feed, UF cable or THHN in a conduit, into a subpanel, and treat it as a subpanel.