Sometimes this works, sometimes it doesn't... give it a shot.

Browse to the location of the desired printer's server.
Right click and select Properties
Click on the Sharing tab.
Click on Additional Drivers.
Add the x64 driver to the list. When you're done, it should say YES in the installed column.

You should now be able to connect to the printer.

If it doesn't work, try installing the entire Lexmark software suite. You can tell it, during the installation, that the printer is located on the network..Report back if that helps.