same staff different context

[David Bobroff]

I've been experimenting with some things to try to deal with a
percussion problem.

I want to change between melodic percussion (those which produce
definite pitch e.g. vibrapbone, tympani, marimba, etc.) and non melodic
percussion (temple blocks, congas, tam-tam etc.)

I want to keep this on a single staff.

It seems that the two contexts can't share a staff.  Even my experiments
with \partcombine result in two staves.

I've had success with assembling music in "layers".  I was thinking that
this would be the way to deal with this problem as well.  I would put
all the pitched percussion in one layer and the non-pitched stuff in
another and just put them together with << >> as I do with other
things.  But, the problem appears to be the inability of the two
contexts to share a staff as noted above.

There must be a way around this.

-David