First:
On the Wood Magic auto support generator thing in the editor, make sure that the "catwalks" and "handrails" tick boxes on both sides are UNticked, leaving just the supports. And then click to create the supports.
Second:
Now, your coaster should be supported in the normal wooden coaster supports, minus the handrails and catwalks. In the editor, highlight all of the supports and then change the supports into the Steel L Beam (it's one of the buttons at the top of the screen, or double click on the supports. Don't know, not got the editor in front of me atm).
Third:
Now you've got just the supports of the coaster, but instead of being wooden, thay are made from the Steel L Beam. Go back onto the auto support thingymajigger, and now swap the tick boxes over (tick the handrail and catwalk boxes and UNtick the supports box). Make sure that you also UNtick the "clear previous supports" or whatever it's called. This way, when you click OK, it will leave the previous support structure alone and just add the catwalks and handrails.
So now, you should be left with a steel support structure, with wooden handrails and catwalks. (if I haven't missed anything important!
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