Yes, it does feel awkward at first, but it won't take long before you're not even thinking about it. I use both hands and pay no mind to the sporran.

It's a bit more difficult if you are entering a higher-clearance vehicle with a step bumper, eg truck. I first stand with both feet on the step. Then I put my right leg onto the floor board, while supporting my upper body by with my right hand on the steering wheel. Without lowering myself onto the seat (and thus messing up the pleats), I put my left leg onto the floor board. This leaves me with both legs holding my nether regions above the seat and my back supported by the seat back. I can then use both hands to sweep the pleats while I lower myself onto the seat.

It's a lot harder to write about than it is to actually do. It just sort of comes naturally if you keep in mind that you do not want your pleats to touch the seat until you are in (an almost standing) position to sweep before you lower yourself onto the seat.

One additional advantage of this technique is that when you do it in public, you often draw both a crowd and applause. Just smile, but don't try to bow.