I wrote a simple relation to deal with the connecting job in relation constrain.
Here you can download it.
Right now it can only connect one slot at one time. but it is enough for me.
Basically I use it while do the stabilized Markers in motionbuilder.
# 1. Creat a Relation Constrain named "Relation". and Drag sender and receiver onto the relation panel.
# 2. Execute the script.