I *think* I have answered my question... If somone can confirm or deny it would be appreciated.
Labview *only* works with Web Services via a wizard that creates a .Net interface.
The constructer reference of a .Net assembly can not be switched switched out because (I don't know why... the rules of .Net? The rules of LabVIEW? Other? Either way the reference can't be switched.)
I tried this in LabVIEW 2010 via an evaluation version and I had the same problem (Invoke nodes broke when Constructer referencs were changed).
I guess the way around this is to make sub VIs and only pull data from the DB, one for each data source. The VI should have no other functionality to simplify the copy/paste from DB1 to DB2, DB3... process.