Passport cards--http://travel.state.gov/passport/ppt_card/ppt_card_3926.html
However, the US Embassy (London) says you'd have to apply by mail-and you'd have to send your passport with the application. Which, well, defeats the whole point!

If DVLA will accept a US Passport Card, maybe it's worth getting in touch with the Embassy to see if they'll allow you to apply in person
OR! GET A SECOND PASSPORT! I think because you travel so often for work, (and can likely prove this!) they will allow you two:
Second Passport You'd apply in person in London.