3K owner here. And, yes I know exactly what you are talking about. Like you I use registrations extensively. Unlike you, I do not use OTS. Why? Because it changes more than just the R1 and R1 voices in your custom built registrations. Many things from style parts to multi-pads will be affected.

If you dedicate one bank (up to 8 registrations) for each song you build you can customize to your heart's content. Styles can be changed within the bank of registrations and by setting it up properly you can avoid any sustain residue or problems such as you mentioned.

Granted, it may not be as easy to accomplish as on the G-70...but it is do-able.

Eddie