Start navigating a course while in an activity?

Does anyone know if there is any way to start navigating a course from within an activity? Today I did a couple of way marked MTB trails and then followed an unmarked route I had prepared using the course option however I couldn't work out any way to do this as part of the same activity. In the end I just stopped the current activity, saved it and started a new one to follow the course but I would rather do it as one as it was all part of the same ride.