Maybe I'm not getting the big picture here, but if all you want is to open several .dsw at the same time there is an alternative way.
MSDEV opens the .dsw files in the same program instance because is using DDE in the default option for the .dsw file types. If you want to open each .dsw in a different MSDEV instance do can do the following:
1.- In any Explorer Windows goto View->Folder Options and select the "File Types" tab.
2.- Look for the "Project Workspace" type and click in the Edit button.
3.- Now select the "Open with MSDEV" action, and click on the Edit button.
NOTE: before doing step 4 write down the DDE parameters in case you want to undo your changes!
4.- Un-select the "Use DDE" option and click OK.
You can get fancier and add a new action ("Open with new MSDEV" for example) without the "Use DDE" option and set it as the default option. Now you will have the two options in the .dsw context menu (when you right-click on a .dsw file in Explorer.)
Thanks to Tim Stubbs for sharing his work and effort.