If you want the car to actually look decent, you could use bondo, sand it down, and re-paint. Then it won't look as if it were tacked on. Use an exacto knife to cut a small enough gap to open the hood/doors/ect, while preventing any significant disturbance to attached airflow.
it will crack.
don't waste your time or time will waste you
I just caulked the seams, then waited for a day or two for the caulk to dry and then used a razor blade to slit a line down the caulk so I could open things that needed to be opened (doors, hood, gas cover, etc.). If you are careful with the razor work, the slit is completely invisible until you open the door, etc. Fortunately my car's color is white and matches the color of white caulk. The total FE improvement due to caulking the seams is probably minimal, but every little bit helps.
slice the caulk at an angle (under cut) and you end up with no gap - are you allowing for flexing of the body? If you tape over a gap with the adhesive only on the upwind side then you can still open everything. Make the tape a flap. I think teflon wax would help more . . . seems to work for airplanes.