What is your selection criteria (formula from the Select Expert)? I would do something like the following:
(
<existing select formula>
)
or IsNull({FirstTable.SomeKeyField})
Note where I put the parentheses - this is important or else it won't work correctly. Basically when you use a key field that always has data in the first table, by looking for it to be null, you should get the data from the second table even when nothing matches the regular selection criteria for the report.
-Dell