Union Query as Lookup Source

I'm doing a "contact" ID and name combo box lookup to attach an ID to a "work step" record.  The contacts are all in a single contacts table, but the lookup source needs to draw from three separate "feed" queries on the contacts table (to knock down the number of contacts to paw through).   The lookup just grabs the ID, so there's no effect on the source data.  There is possible redundancy amoung the three feed queries, but they can probably be ignored.   I'm looking for a general approach...
>  big union query?
>  or, on "requery" event (prompted in different ways)
    >  build a temp table as recordsource using the feedqueries and an append query, or recordset logic in vba.

I could go either way but was hoping to not have to go through trial an error learning on which would work best or most easily.  May be an easy answer but only so many brain cells left...

Would either work?   Is one more reliable?

Any suggestions on a general approach for this would be appreciated.

Thanks!