Wyse is working with different code bases. So it is not easy to determine which version you would need.
I know that this feature was implemented in 5.2.0_62 in june 2008. So each firmware that was released after june ’08 should have this feature included.
But, and there is always a “but”, as 5.x code base isn’t supported anymore I doubt that this feature was ever included in 5.3. You can try 5.3.0_023.
CG