In fact, it would be even cooler if I could have not a page reference, but plaintext preloaded, like
<inputbox> type=create width=24 buttonlabel=Create me! preload_plaintext={{person}} </inputbox>
This means preloading a template? This is possible. Look here: http://meta.wikimedia.org/wiki/Inputbox#Preload
I have read that, of course. I would like to have "{{person}}" preloaded in the page, not the content of Template:person.
Cheers, Ingmar