My wife's Epson RX680 is used by everyone in the house via printer sharing, so she gets pretty annoyed when the Epson Print Monitor pops up suddenly on top of whatever she's working on. Today she made it annoy me enough so that I had to figure out a proper fix. The fix is to tell Launch Services to launch it in the background.
This requires editing a file within the application Epson Print Monitor, so be sure to back this application up first! The file to back up is /Library » Printers » EPSON » EPW » EPSON Printer Monitor.app.
Once that's backed up, Control-click on it and choose Show Package Contents from the contextual menu. In the Contents folder, you'll see the Info.plist file; we're going to add a new key, LSBackgroundOnly, specifying that this should be true (i.e. launch in the background).
I use the pico editor from within Terminal:
<key>LSBackgroundOnly</key>
<true/>
For clarity, here are the key above, the new key and the key below:
CSResourcesFileMapped</key>
<true/>
<key>LSBackgroundOnly</key>
<true/>
<key>LSMinimumSystemVersion</key>
<string>10.5.0</string>
Save the changes; if using pico, Control-X and y for yes, then hit Return.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20090830194413248