I've actually found the following information but still not solved the problem. On Qlikview's Help page under "statistical distribution functions" it states:
The statistical distribution functions described below are all implemented in QlikView using the Cephes library. For references and details on algorithms used, accuracy etc, please see http://www.netlib.org/cephes/. The Cephes function library is used by permission."
In my net searches I actually found that the Cephes library is where you can find a MYSQL script for creating Beta distribution (and hence finding the inverse of Beta distribution).
Has anyone called on this library of functions before?