GPU computing on MacBook Pro

I am trying to work with GPU computing on MatLab on my MBP, OSX 10.9.3 . My MatLab version is R2014a. This laptop has two graphic cards: one built-in (Intel HD Graphics 4000 graphics) and a discrete one (NVIDIA GeForce GT 650M 1024 MB). The OS automatically switches from one to the other.

My problem is that when I am using the NVIDIA, too much memory is taken by the OS, and I cannot do any operation (if not with really small arrays).

Does anyone know how to have my laptop using the built-in Intel graphic card while reserving the NVIDIA for MatLab's computations?