This explains that IBKR allows it (see below).
However, I don’t know “what direction” it would work. eg. With a UK stock such as BP my guess would be it is likely that you can only convert from the USA ADR to the UK listed stock and not the other way around.
For example, for Alibaba would we be only able to convert the Hong Kong stock (secondary listing?) into the NYSE stock (primary listing) and not the other way around?
Also, I guess that we would have to have access to the Hong Kong exchange first.
It may also be quite expensive to convert, looking at the fees.