I would question whether these are projects - if anyone can book time to something, without project/resource manager approving, that has got to wreck the project's budget, plus one can't plan who is going to do which tasks on the project. Perhaps this is more of an Agile environment, where resources can see what needs to be done and pick the work up by themselves?
If not, may I suggest using the "Other Work" object in CA PPM instead of projects - much less admin overhead. You could still use David Morton's suggestion, just use the gel/xog script to allocate resources to Other Work instances rather than to project. If needed, one can still do some allocation level planning with Other Work, unlike Indirect.
The time to look at using other objects in CA PPM besides projects is now, sooner, not later. Trust me, if you start using projects for things that are not projects, you may be stuck for years. We started with projects in ABT, wishing for other objects to use. Now that we have them, we are still stuck using only projects! Change is hard. Waiting only makes it harder!