I tried the PB syrup with splenda and cinnamon in the M&BS oatmeal, and they were terrific! I basically filled a measuring cup to 1/3 with the vanilla and PB syrup and water (I used lots of syrup!), and then slowly added that mix to the oatmeal a bit at a time so I didn't make it too watery. I ended up not needing a good bit of the liquid, so I think they key to avoiding the silver dollar syndrome is to add the liquids carefully, and don't feel bad if you end up throwing some away without using it. Then the cookie "dough" set up nicely, and when I spooned it onto the cookie sheet, the lumps pretty much stayed where they were, with no spreading. (I made 6 cookies out of the dough.) They flattened a tad in the oven, but not much-- and I cooked 'em for 15 minutes. At 10 mins they were way too soft.
They still don't quite taste like a real, fat-laden oatmeal/PB cookie, but hey, I'll take what I can get!