The only option to use the iPod/iPhone slot connection on the SS25 is the MidiBridge app and because Apple have removed it, I think the only way is to restore the app from a backup or if you have the IPA file somewhere.
Alternatively you can use the USB port on the SS25 (see below)
Actually, there is another way - you can use a USB mini cable with Apple's Camera Connection Kit (CCK) and connect the USB cable to the side of the SS25 and back into the iPod via the CCK. That will then show up as a CoreMIDI device and you should be able to use it in any app that supports CoreMIDI. You'll need a 30 pin CCK for an iPod4G and of course it won't sit in the SS25 ipod slot but it will work.