It would be possible when you cheat a bit. First of all your App needs to be associated with the filetype you want to be able to doubleclick. If this once works, you could do the following:
Use the windows Api (FindWindow I guess) to see if your Tool is already running (Using Apptititle to recognize it). If the tool is already running, write a special command to the clipboard. Something like
Myapp:magic31415926-1.2.3.5.8.13.21/open>>path\test.mp3<<
In the same time the tool that is already running will check the clipboard frequently. If it detects some special command (likethis example containing a magic key code and a access path etc.) it will open the test.mp3 file, then it will erase the clipboard.
The second app process, that didn't really open the tool and the test.mp3 file then simply exits.
Well this is the way I would try it, tho it's kind of a hack.
Use the windows Api (FindWindow I guess) to see if your Tool is already running (Using Apptititle to recognize it). If the tool is already running, write a special command to the clipboard. Something like
Myapp:magic31415926-1.2.3.5.8.13.21/open>>path\test.mp3<<
In the same time the tool that is already running will check the clipboard frequently. If it detects some special command (likethis example containing a magic key code and a access path etc.) it will open the test.mp3 file, then it will erase the clipboard.
The second app process, that didn't really open the tool and the test.mp3 file then simply exits.
Well this is the way I would try it, tho it's kind of a hack.