Turn on wing deice, worked for the dc10 over russia
You need to be careful using wing anti-ice above it's certified altitude, unless the airframer has previously approved it. Wing anti-ice takes quite a bit of bleed air, and on some installations using that much addition bleed at cruise altitudes can cause problems with engine operability (e.g. it won't accel) and/or cabin pressurization (not enough bleed air to maintain cabin altitude).