Another easy way to do this -- if you are out in the middle of the water (I did this in the water due east of Eagle's Nest and north of the volcano), various boats will cruise up to you, presumably to rescue you. Look for a white dinghy-looking boat called the Jaeger FSJ 7, and get in.
Take that boat, increase to a cruising speed in a straight area, and then hit "A" to go to stunt position, "A" to use parachute, "A" to freefall, and "A" to jump to vehicle. You can repeat this over and over, as it seems the boat will continue at a regular speed if you cycle this properly. You have to be good with the timing, but it's not super difficult.
You do not have to go directly from parachute to the vehicle, but you can do that (for a split second) as well.
Hat tip to Seraphim Needed and his solution for the general idea.