Thanks for the very clear explanation!
We have actually tried the rpath approach in the past, but ran into some problems depending on the platform/configuration people would have. From the various reading about rpath and LD_LIBRARY_PATH on the internet, there is actually not a better way. Each of the approach has advantages and disadvantages, and since currently very few people are complaining about similar issues as you have, we are reticent to changing the way we did until now. We might give it another try again, but this is always risky to change something that works relatively well ;)
Have you tried to recompile the client application yourself with the said rpath settings? The source code of the client application to V-REP (i.e. the vrep executable) is located in programming/v_repClientApplication. The source code is actually a single, very short program, so compilation should be easy.
About setting the rpath in a Qt application this read could be helpful.
Cheers