1. Assign Sequencer 1 (for example) to OscAllFreq
2. Set step 5 to Reset
3. Set step 2 to 1
4. Set step 3 to 2
5. Set Seq. Trig. to Key Step
6. Assign Modulator 1 source to Sequencer 1
7. Assign Modulator 1 destination to OscAllFreq
8. Set Modulator 1 amount to somewhere between -127, where the "sequenced slop" will have no effect, and -110, where it's probably too much.
9. Optional, set a very slow triangle LFO to modulate Modulator 1 by a small amount.
Now each voice will be detuned somewhat, consistently each time it is played, as though its voice card had drifted. You can do the same thing for individual oscillators, as well, of course.