Find and run skype v3.8. Login as usual. Check "auto sign when starting skype" (i.e. save password option). Restart 3.8 again. Now, in you config.xml profile will be "Credentials2" block with your skype signed public key. Now, run skype v5.5 version. It will login automatically, and will not bore about outdated version and will not signout you. If it expires in 30 days, repeat this steps.
P.S. If 3.8 not logging in, use latest skype 6.18 version for signing and getting good credentials.