Is there a way to do equivalent of macro substitution in SQL-Server

I have a stored procedure for a specific database to retrieve 101 records from a table (50 prior to given key, key record, 50 after the given key value)

Since you can't use the command

USE (other database name)

within a stored procedure, I need the ability to tell it which database to get the data out of, and also for create cursor/fetch.

ex:
ClientDatabase_A - CustomerTable
ClientDatabase_B - CustomerTable
..
..
ClientDatabase_C - CustomerTable

Also, depending on the parameters passed in (which I already have under control), I may need to look at a different table and fields
for selection. The principle can still apply but for "inventory items" instead of the CustomerTable..

Any help would be greatly appreciated,
TIA