Nope. There's no way for you to hide the warning - and that's a good thing, because there's also no way (yet) to make an AIR app that doesn't have full access to the user's file system. In theory, any AIR app could delete random files without telling the user, so the warning is quite necessary. I believe that restricted AIR apps are something Adobe is planning for the future, but nothing so far.
The only think you can control in that dialog is, if you sign your app with a certificate that is trusted by the user, then your name will appear in the "Publisher" field. Otherwise it will be "unknown".
(Note that if the user does install your app, then in the future when they upgrade, you can substitute a custom dialog. But for the initial install you are stuck with the standard one.)