Well, DMR wingbars, the MX style ones with a crossbrace come as standard with a shim to fit a standard MTB 25.4mm stem (the tube dia is sub 25.4mm) I ran them for years on my MTB without any problem so shimming isnt actually a problem, if you can find the correct size shim then go for it.
As your running flat bars you wont have much twisting force either, just go for it…
remeber this shim wont fit, but just to show the principle is sound.
Features:
• Bombproof 4130 Cro.Mo Steeel Riser Bar.
• Welded cross-bar design for heavier riding styles including, jumping, trails, downhill, BSX ect.
• Wingbars come with a shim so can be used with burly BMX stems 22.2mm or standard MTB stems 25.4mm