[aerohead]

If you intentionally leave an open gap to accommodate the vertical movement of the axle,you can construct the pan superstructure 'before' and 'after' it.
And the aft portion can be designed as the diffuser.
With the pan on,the majority of energy will be maintained,and flow will be directed to 'jump' the gap.
Yes there will be a local perturbation,but most of the flow will just blow on by.
Later,you can deal with the axle area as a fine detail if you like.
That opening will provide an extraction point for hot air.