Hi canadagoose-
There's not currently a built-in feature for this but we do have an AppleScript available to do this. You'll find it in our scripts package here:
http://www.omnigroup.com/ftp/pub/sof...fulScripts.dmg
Use either the 'Collapse To Level X.scpt' or 'Collapse to Level of Selected Item.scpt'. You'll also find instructions on how to install the scripts in the OO file included in the package.
If you need anymore help with this, please let me know.
--
Derek M.
Support Engineer
The Omni Group