I took this from
www.snakepit.org - slash fan site
For live appearances, the JCM SLASH Marshalls are used for a dirty sound. For the dirty tone, the SLASH recommended settings are: Presence: 7, Bass: 7, Mid: 4.5, Treble: 7, Output Master: 6, Lead Master: 10, Input Gain: 6.5. The JCM SLASH Marshalls are used for a clean sound, too, when modified with KT88 output tubes. The SLASH Marshall should be tuned this way for the clean tone (SLASH recommendations): Presence: 0, Bass: 9, Mid: 3, Treble: 5 1/2, Output Master: 10, Lead Master: 0, Input Gain: 4. All tubes are groove tubes.
hope it helps - personally i wouldn't be able to just buy a new set of pick up's (they ain't cheep) so maybe an eq tweek like above might give you a good enough approximation.
8)