it depends upon the monopod as to how it is done. Some, like Bogen, come w/o heads and one merely attaches a ball head to it. Others, like Slik, have an internal ball head.
Either way, just rotate.
It is easier to see than explain.

This is true, and thanks for the reply, but I was looking for something that would attach to the end of the lens itself, that would allow the camera to pivot to those orientations.

I have seen this action mostly of the lenses that have a built in tripod ( 400 -600mm ones, I think )

Thanks again for the response, will keep that option in mind

Longer lenses will have a tripod collar that has a 1/4 20 fitting so that the screw from the plate is accepted. The collar rotates to any angle desired.
There are some gimballed heads that allow the camera to rotate around its own axis. have you looked at those?

Ronk,

Most of the pros use an "L" bracket quick release, which makes it easy to change from horizontal to vertical without affecting the position of the camera lens centered over the monopod. The "L" screws into the camera tripod socket and the "L" has two quick release connectors at the ends of the "L" at 90 degrees, and interface with a tripod/monopod matching quick release base. These "L" bracket quick release accessories are made by companies like Sinar and are well engineered and machined if they are to work effectively, and are quite expensive.