Body forces: applied only to every particle or selectively ?

Hello everybody

Is it possible to restrict the application of a body force (gravitation field force, fictious viscous) to a subset of particles, for example particles that have been tagged with a certain label when created with the LSMGenGeo library ?
I understood that once created, the body force applies to all the particles, indifferently. For a field, like the gravitational one, that's correct.
It would be nice if different body viscous forces could be applied to different subsets of particles.

The reason behind my question is the following:

I'm modeling a 2D shear cell made of groups of bonded particles, representing the shear plates, and an ensemble of unbonded particles, representing the sheared granular layer.
The viscous body force is important for the bonded blocks, shearing past each other, but less for the granular layer.
It would be very useful to apply two different viscous body forces to the two different sets of particles.

Thanks for your help and support

Best regards

Michele