If the printer is a network printer, capturing to it should be as easy as going to a command prompt and using this command:
NET USE LPT1: \\ServerName\PrinterName
You can create a plain text file with that command in it using NotePad, then save / rename the file with a .CMD extention. Drop it in your startup group.
The potential problem I see is if the shared printer is an inkjet or cheap laser, your DOS program may not be able to use it. Many modern printers now rely on windows to actually render the page (so-called "GDI printers"), and can't handle simple being snet print data.