midi merge logic 8

ok, i am coming from pro tools here. i want to record a midi overdub into an existing region without creating a new one overlapping. in pro tools, there is a "midi merge" button in the transport window. this allows you to add notes to an existing midi region without creating a new track. i have figured out how to record midi on another track and merge after the fact, but, specifically, this is what i want to do.

1st pass, record bass drum and snare drum
2nd pass, record hi hat
3rd pass, record cymbals etc.