If I understand you correctly, you could do it with AppleScript.
I think you mean "be able to connect/disconnect all of the configurations in a submenu with one command".
Most users connect to only one VPN at a time, but for someone who connects to several VPNs simultaneously, I can see how that would be helpful. An example would be an IT worker who connects to several servers at one time. (This would require very carefully constructed configurations so the routing would work correctly).
Note: I'm not talking about "nesting" VPNs, where you get to one VPN though another, because these usually (always?) require that the VPNs be established in a particular order.
You should be able to do this
using AppleScript, assuming the AppleScript takes the submenu name as an argument:
Get the list of configurations
For each configuration:
If the configuration is on the specified submenu, connect it (or disconnect it).
The configuration name of configuration "bar" in submenu foo would be foo/bar. (It's possible it is "/foo/bar", but I don't think so. You'll have to try it.)