To do the elbow as the first hit, you have to proxy cancel the bushin chain first. That sets a trigger that switches your FP to the elbow.
Ground Normals switch the trigger back and makes your FP a regular FP again. But air normals, throws, ground specials, VC activations, and ground supers don’t switch the trigger.
To do it, you execute the bushin chain, but cancel the last hit (the RH) within the first few frames of it’s animation (meaning, before it hits) with a special or super. Because you canceled the RH, the game is still holding onto the trigger that makes your FP’s the elbow move. So the next FP you do will come out as an elbow.
So it’d be like: JP, SP, FP, push RH and immediately cancel
Next FP you do will be the elbow (assuming you don’t reset the trigger before your next FP).
I’d recommend buffering the special or super motion during the FP. Then hit RH and immediately hit another button to cancel the startup of the RH, like a kara-cancel or rollcancel.
It’s also possible to cancel the RH into a level 3 kick super (which requires you to push RH) by tapping the RH once as fast as possible. The button input will activate the RH and the negative edge will activate the super if you were able to release the RH button quickly enough.
This kinda belongs in the Guy thread, yeah?