OK, I've said it many times so I'll be breif...
Transformers that need to fit under the carrage will need to provide enough KW to the three phase transmission system used on the 22x series units to be able to be used.
1) Transforming from single phase 25kv AC to three phase aint easy, it's very hard and needs some very beefey solid state electronics.
2) Such a device to be able to power a whole unit will not fit under one carrage of a 22x unit
3) Even if such a unit could be fit inside the area needed, it wouldn't be desirable to do so, converting a 4 car 220 or 221 to a 5 car electrodiesel unit with one panto/transformer car is pushing the limits of what the distribution system on the units would be able to take. As a general rule of thumb, the current can travel two carrages.
Therefore:
4 car units become 5 or 6 car units (Much easyer to provide two 1700kw transformers than one 3400kw one) only one panto raised at a time, HV link cable along the top (as on pendos)
5 car units become 7 car
7 car units become 10 car (or loose some generator cars to the 5 car units to make a standard fleet of 8 car units)
Because of the way the control system works (and I aint typing all that again), new generator cars may have any type of diesel or gas engine fitted, without worry of it affecting the others, it would simply make for more complex servicing, witch isn't desired.
From the point of view of the TOC, it is more carrages, and less diesel costs. But it is at the trade off of less power to weight when on diesel only, but, again, thanks to the control systems that are used on these units, as most non-electrified lines (post GWML wires) will have a linespeed of 110 or less, this won't affect it, only the accelaration between approximatly 90 and 125mph.
In any way, conclusion from this being able to be done is:
Wire Crewe - Chester
Wire the Midland Main Line
Electrodieselify the 22x fleet
No longer have a requirement for ANY bi-mode IEP units.
Oh and PS: Pan up or down on the move needs very high tensions in the cables above, on the fly is not a good idea unless the wires are designed to do it. Such as on the Fawkham Link