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Thanks for asking.
This should be possible (but error prone, seeing as the Cmd-Tab OS X tool has no API for requesting status and disappears on more outside events than just the release of the keys) with a dedicated Behaviour using Apple Script.
It would, however, mostly just be an unnecessary effort, since you can already switch between applications using Remote Buddy. If you want to tune Remote Buddy for use primarily as a dedicated switcher/launcher between a select number of applications, here are some ideas:
1) If you want to access the root of the Remote Buddy menu (where, by default, all Behaviours are listed) when you press Menu, you can select the respective action at Prefs > Mapping > Global Mapping > [Menu button]
2) If you want to limit the layout of the root level of the Remote Buddy menu, you can do this at Prefs > Menu by creating your own profile, customize it, then select it to be used as default
3) If you want to activate/switch Behaviours with a single button press - and not descend into the application's context menu - you can achieve this by changing the respective option at Prefs > Menu > Size & Appearance.
Best regards,
Felix Schwarz