Flatten 3/4" She Oak board?

Hello all,
I've made a red She Oak baffle for a loudspeaker face, and I was about to glue it to the maple veneered MDF carcass when I noticed it is bowed across it's width. It is about 18" long by 6" wide and is warped such that ends are upturned about 0.5mm at each end -- enough to be noticeable. Is there any way I can flatten it without using a planer? Wetting, clamping, steaming or some kind of ritual sacrifice perhaps?
Thanks for any advice,
Thomas Hood

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