That would be a huge mess of dust and chewed up edges. You'd need a proper slitting setup (like the manufacturers and aftermarket converters use). There are some 'dry lab' papers (i.e. specific conversions of inkjet papers), but I think the widest they go is 8" rolls.
I'd start by asking why you can't cut the thing down after printing (is it extremely long?), and only if the answer is definitely negative would I start looking at roll conversion services (they supply various industries, there'll be something quite local to you I bet) or asking the paper manufacturers what the MOQ for 12" rolls are (more than you'd hope, less than you'd think - usually).