I've been thinking about this one all day, "how do you practice without practicing."
Hard one indeed...but here are some suggestions....
Talk to your church, see if they will let you in to practice on the organ. That's where I would start....
MIDI pedals, the same dimensions as those that come on the Hammonds are available from Hammond and Roland. Those midi into your own keyboard and there ya go. The added advantage of buying these would that you can slowly build up a two manual pedal system with the XK3, check out this link:
http://www.hammondorganco.com/product_set4.htmA less expensive and quieter solution would be to try to buy some pedals off of an old Hammond organ.
...of course you won't get any sound, but at least you've got something to work on, and you can practice what is effective for me...saying the name of the note as you touch the pedal.
An even less expensive alternative would be to build your own set of pedals, a model of the pedals that you play on-but you have to be a pretty good carpenter to do it to get the dimensions right. Again you won't get any sound, and this would be the most time consuming of the 3 methods, but if you get the dimensions right, then using the practice method above, at least you're getting some foot time with the pedals.