Assign HU (Non-Assigned) to Shipment

Hello Experts,

I have seen couple of threads on this issue but didn't get final answer.

Is it possible to assign previously created HU directly to Shipment? Am able to assign it to delivery, but when am assigning to shipment getting error '

HU XXXXX is assigned to an object that cannot be processed here. Message no. HUDIALOG155

We have a requirement to Pre-Create HUs in HU02 (or) HUPAST, first followed by assigning them to Shipment. Is this possible in Standard? If not, did anyone developed custom code (Exit / BADI) to overcome this issue?

Thanks!!

Surya