If you are using ADS 10.1 client or later (requires server or later) then you should be able to pass "extra parameters" and set the EncryptionPassword.
Help file for AdsConnect101 http://devzone.advantagedatabase.com/dz/WebHelp/Advantage11.1/ace_adsconnect101.htm
In ARC you can edit the connection properties and add this to ExtraConnectString
In Delphi the connection component should have a Connection String I belive
I'm not 100% sure this will work (is exposed) in all languages/drivers