If you choose to stay in an uncorrected altitude of 3000ft, than you have to start your descent later and apply the cold temperature correction on your FPA.
So -20 gives you 3,5*0,04= 14%. This means if you start your descent in DUS at 7.6 NM with an FPA of -3,4 you should be fine.
We only have to correct altitudes below the corrected MSA. So in this case all below 3192ft