How to setup my stretchy bone for muscles?

Pretty new to ue5 and looking for some advice on how to set up my character…

So I have a custom skeleton retargeting the ue5 mannequin, on the skeleton I have a number of bones that stretch across joints to act like muscles (like a stretchy bone with one end connected to the chest and the other end connected to the upper arm to emulated the pec chest muscle)

The problem is, the ends of these bones/muscles were connected in 3ds max via animation constraints and I don’t know how in ue5 to join up the end bone of the pec muscle to the upper arm for example so that the pec bone will stretch whenever the arm moves.

Any advice would be great