dicklaan apologies for the confusion - yes, the first workaround should work (though keyframing the envelope may be a bit tricky)
Regarding selecting the target of the attachment - we don't provide a mechanism to directly specify the target point, though, if you paint the attachment weight on the target object, that will limit the closest point search to only those areas where the attachment weight is near a value of 1.0
I hope this helps!
-jj