Yes, that's what I was getting at. Various temporary projects have been planned using slips like this before.
How can it be "anonymous" when publishers are instructed to return their pledge slips to the COBE or another elder?
Well, I don't think the letter gave instructions on how to get the slips back from publishers. Some elder bodies may be asking for the slips to be handed back to a brother (that still doesn't mean he is (1) looking at them when they're handed to him, as opposed to just stuffing them in his briefcase, and (2) actually making a record of what each person wrote), but in some halls the slips will probably just be returned by placing them in a contribution box.
In my congregation, we aren't doing slips at all because there was already a mortgage, so the brothers are just going to continue giving that amount to the KH fund.