How can I prevent a part from being added to any stage?

In Kerbal Space Program many parts, typically engines and separators are "stagable", in that their activation can be tied to a stage. However sometimes I have stagable parts that I don't want tied to any stage, for example Sepatrons that I want to use to use as part of my Abort action group. The game seams to automatically put these parts into a stage, is there a way I can prevent them from being staged, to be activated as part of an action group or manually?

As far as I know there is no method or option to prevent this default behaviour.

Workarounds:

As Elias said, one method is to put these modules at the top of the staging queue so they don't get fired, but for that you must make these groups first, or move them manually to the top when you do them last. This leads to...

Simply remove them after they are being added from the staging queue. When you build these parts last, just completely remove the last (first to be activated) part of the queue.