[Gray Adams]

There's all kinds of little tricks or things you can do. Reference geometry like planes and axis that are bound to the electronics can be easily mated to your layout board. Or you could try to find some feature on the electronics component model that you can use. Like if there's a hole or a flat surface in the center of the model, you could use that for mating and just set the mate offset distance to be whatever you need.

Blocks that approximate the size of the object while being really, really simple are great too. Depending on how complicated your layout is going to get this might not work, but in all likelihood 2 rectangular blocks could replace a jaguar for modeling purposes.

You could also just leave the models unconstrained and drag them around and then lock them in place. It's not really a great way to do things, but for free form layouts I think its ok.