If you need to always provide the same arguments to an application, I strongly suggest you create a Windows Shortcut to that application, where you can customize arguments, and make your slimLAUNCHthis hotkey open the shortcut. What slimKEYS could do is help you create such shortcut files. I prefer explicit shortcut files, as they may be useful to you elsewhere than in slimKEYS. Then again, it wouldn't be that hard for me to add an "Arguments" and "Working Folder" option to a slimLAUNCHthis hotkey. Others have a preference?
If you need to provide different arguments everytime you launch this application, you can check the "Show extended launch options" checkbox in the slimLAUNCHthis hotkey config. This will let you enter custom arguments everytime you launch this application.