Litopia

Hey, you could write back to them in a few months, and say: Thank you for requesting my full MS. Please find attached my novel. I'm pleased to hear that you think it's a unique and highly sellable concept. I look forward to hearing from you.
By the way, I'm kidding ... am I kidding? … Me? No, never … Or...

I would do precisely what @Barbara said, and if they come back to you and say we never asked for it, you can say, "Really? Oh... I thought that's what you meant" and hey-ho, nothing ventured, nothing gained. On the other hand, they just might actually read the MS. Call it a "Crossed Wires" communication device

That is...very tempting, actually...