Unless this lift is designated just for this vehicle, I wouldn't worry too much about it. I've been in that situation many times...a stretch limo a few weeks ago...just chock the front tires(the rubber chocks work best) and set the park brake. It'll be solid enough to even R&R the trans or engine.
Even if the lift WAS just for this vehicle, you could also just use a ratchet strap or 2 and secure the vehicle to the front crossmember of the lift. Too many ways around this minor problem, even when safety is the #1 priority. You seem too sharp to let a minor inconvenience like this cause you to want to get rid of it already. Try it out a few times before you unload it for a loss.
edited to add...
the only way I'd get rid of this lift is if it had the built in sliding jacks. You wouldn't be able to lift the rear axle using them...based on what the picture shows.QUOTE]
I have a rolling jack coming after the first of the year, and you are correct, it will not lift the rear end the way that it is.