If its to order the car then their is the option (dealer permitting) to have the sales person bring the car to yourselves for a test drive after completion of a test drive the sales person can take any necessary information, should you decide to take it further and order then the dealership has your info and is not in breech of the rules, we were offered this option as it was better to test drive at home on familiar roads rather than the busy city centre where the dealership is based. as well as being a named driver you may also want to look into becoming a “Nominee” or in exceptional cercomstances an “Appointee” this makes things easier when dealing with things on your wife’s behalf.
https://www.motability.co.uk/about/how-the-scheme-works/information-for-carers-and-appointees/