It would be great if you could :) but to my knowledge there is no way in MMM of isolating say the bass line in a track unless there is a section of the track that you can sample that only features the bass... then you can repeat or loop the sample for as long as you like. You can reduce the influence of other sounds that are in a different frequency range by filtering  - but it will not be entirely satisfactory.
hope that helps ... better still hope someone knows how to do it !