What I ended up having to do was this, inside the \score block:
\new Staff = "Staff_oboeDA" <<
\transposition a \transpose a c << \global \oDAMusic \keyandtempo >>
>>
(\keyandtempo is another variable that contains all the key and tempo changes, and consequently has to be within a multi-voice context with each instrument's variable).
But that worked! Thanks! That's exactly what I needed.
Cheers,
A