Similar to what Rick Potter posted, I use a long skinny piece of ash to push the stock through. The guides are pushing the stock down and toward the fence, so you just need something to move it forward. The push stick needs to be thinner than the stock, because it sometimes needs to pass under the guide wheels.
I use the riving knife, but sometimes have to remove the blade guard for really narrow stock.
I recall watching some Jessem videos that (I think) demonstrated how to handle narrow stock. It's a little nerve wracking at first, simply because you're used to having to apply downward/sideways pressure with a normal pusher.