This is well covered on the s4 tuning wiki 

but here goes, i think this info may apply to you:

If you have removed precats and relocated your rear O2s, and you want to keep the sensors in place and working (to make sure you still pass emissions testing), you may throw an efficiency code. You maybe able to numb ME7's sensitivity (note: untested) using: [51][52]
AHKATMN (0x18672) - leave alone
AHKATMX (0x18673) - set to max
AHKATS (0x18674) - set to max
AHKATSB (0x18675) - set to max

taken directly from the wiki

He hasn't removed the cats though.

Set these to zero to disable rear cat DTC entirely:
 CDKAT - Cat diagnosis in OBDII-Mode. (ME7.5 vehicles containing CDKATSP AND SPF should 0 these as well).
 CWDLSAHK (0x18663) - Code word for probe aging after KAT[50] (not needed if you set CDLASH to 0)

If you want to remove your rear O2s and cat entirely, also set these to zero:[53]
 CDHSH - Post cat O2 heater diagnosis
 CDHSHE - Post cat O2 heater amplifier diagnosis
 CDLATV - Lambda sensor aging diagnosis (tv) in OBDII-Mode (inverse: EURO-Mode)
 CDLASH - Lambda sensor aging diagnosis (SHK) in OBDII-Mode (inverse: EURO-Mode)
 CDLSH - Post cat O2 sensor diagnosis
 CDLSHV - Lambda sensor sensor interchange recognition (N/A for vehicles equipped with a single post cat sensor, IE 1.8t and certain vr6)

And ESKONF should get you there.