There might be some confusion here, but it does work in 5.5.
Before you attach your mesh you need to check “preserve with bake”. After you right click and select for example “trim right and preserve” you have to delete the key at the end of your sequence.
This worked for me after some trial and error, the mesh stays the position it was deattached at.
If the model doesn’t appear in the render, you might have to make it a spawn able object in the sequence.