IFD540/440 Touch Screen GPS/NAV/COM : OBS mode

I was wondering how to add modified missed approach instructions that are issued that are different than the published.  Typically they start out with turn to heading xyz and climb to 1234 or climb to 1234 then turn to xyz then climb to 5678.  Maybe I'm thinking about this wrong, but I thought the way to do this would be to put the 540 into OBS mode at the MAP with an altitude restriction.  I'd like to add this to the flight plan prior to flying the approach.

It looks like once the MAP is the active waypoint, I could enter OBS mode and select the course, but OBS mode is not allowed insde the FAF.  It also looks like I can't add an OBS course as a future leg in the flight plan and that it can only be used with the current active waypoint.

Even if I could add an OBS course to the MAP in the flight plan, would it be a direct course from the MAP and not include the curve that is typically shown when changing course to account for the turn radius?  The instructions never say track xyz outbound from the MAP, they expect you to turn to xyz then maintain that heading.

What would be the best way to add modified missed approach instructions?