Apple - Choose a default app for opening files with no extension?

You can add a default application for public.plain-text in ~/Library/Preferences/com.apple.LaunchServices.plist.

defaults write com.apple.LaunchServices LSHandlers -array-add '{LSHandlerContentType=public.plain-text;LSHandlerRoleAll=com.apple.textedit;}' '{LSHandlerContentType=public.unix-executable;LSHandlerRoleAll=com.apple.textedit;}'

Restart to apply the changes (logging out and back in isn't enough).

I've added this to a duti configuration file:

com.apple.textedit public.plain-text all
com.macromates.textmate public.unix-executable all

You can do this using Magic Launch. After installing, you can create rules to launch based on various criteria. You need to create a rule for text apps where the extension is blank. You can set up more complex logic if you need it.

http://michelf.com/software/magic-launch/