Adam -- if you do not know the password for the original certificate there is nothing we can do to help you. We do not have a copy of your certificate passwords. If you are unable to use the original certificate you'll have to delete the old app from the store and install a new app, based on the new certificate. This means you will lose history for the old app and existing users of the old app will not be automatically informed of updates for the old app.
Sorry, but this is not something we control, this is how the Android app stores work and is dictated by the Android stores, the XDK and Intel have no control over this app certificate policy.