How to get higher 3.3V rail from Fortron 550W ???

[Stelios]

I just bought a Fortron 550W psu and i'm trying to get a higher 3.3V rail . Inside the PSU are two pots . One for 3.3V and one for the 12V .
The problem with the 3.3V pot is that even if a turn it all the way (zero resistance) the rail can't get over 3.5V.
A friend of mine told me that it is possible to put another resistance in series with the pot , in order to get higher voltages ...
Anyone knows how will i make it ???? My fried has already done it but i have to go to his place and check it .

I just don't wanna do it with the vsense way .

Thanks !