Your problem is more serious than you might realise. The task of transmitting spooled printer data to a specific printer is calls a Print Processor, which sits in the printer chain preceding the Print Monitor. Documentation here: http://msdn.microsoft.com/en-us/library/windows/hardware/ff551771%28v=vs.85%29.aspx
The spooled data can be in one of several different formats, and for some of them it may not be possible to redirect to a printer of a different type. You didn't mention what types of printers you are dealing with.
This is fairly serious stuff: writing and debugging one of these babies takes significant low level skills and understanding of Windows tech.
Edit: There's a good chance the data is in Enhanced Metafile format, and you need to take advantage of the built-in converters to turn that into commands for your new printer.