Since PostScript usually is prefixed with ``%!'', it's easy to educate your spooler to autoselect between passing raw PostScript through to the printer or doing an ``ASCII-to-PostScript'' conversion first. There are many packages that will do this, including Transcript and psxlate.
Unfortunately, many PostScript applications generate PostScript without a proper ``%!'' magic cookie.
The spooler should be responsible for transmitting the ``job termination code'' (a control-D on serially-connected printers) to the printer, not the application. Do yourself a favor and disable (or filter out) control-Ds in your applications and generate them in the spooler. This will be far more reliable in the face of arbitrary input.