Move/copy and configuration is the only way I have found this to work, but be aware mates have to be constrained so as not to have stuff jumping around(using planes instead of faces for the mates).
Paul is right. Move/copy bodies + configurations is probably the easiest path to follow.
1- Create an exploded configuration from the Multi-body part file ONLY. Using move/copy bodies create the "exploded view" of that file only as you want it.
2- Create a configuration at the ASM level, call exploded. Do a normal exploded view of every other part and sub-ASM apart from the multi-body part in the ASM.
3- Set your MBP to its exploded config.
You could also consider creating a subassembly from your multibody part by going to :
Insert > Features > Save Bodies. Tick to save all bodies and tell it to automatically create an assembly for you.
From there you can create an exploded view in the sub-assembly, and then 're-use subassembly explode' at the top level.
Thank you all,
I decided to go with Logan's reply for this one. I will try and experiment with the other method when time allows.