SongSheet includes basic support for Bluetooth pedals such as the AirTurn BT-105.
Bluetooth pedals are seen by iOS as a keyboard with only a few keys. For example, the 4-pedal AirTurn sends key strokes for cursor up, down, left and right. SongSheet interprets these as previous stanza, next stanza, previous song and next song, respectively.
This means that you can accomplish the same thing via an ordinary external keyboard using the cursor keys.
See the documentation for your particular pedal in order to pair and connect it to your iPad. Once connected, assuming it sends up/down/left/right key strokes, it should work with SongSheet out of the box.
Alternatively, for more flexibility, use the free SongSheet Remote app on your iPhone or iPod Touch.