First, copy the entire contents of the /Program Files/Opera Mobile 10 folder into the /Windows folder. It's important to copy more than just the .exe file, otherwise the program won't launch.
Next, use a registry editor to change
Finally, soft reset and you should be all set. There are probably other ways of doing this; please share any other methods you may know.
Update: this method doesn't seem to be working for everyone; suggest you read the entire thread, as Dsixda has kindly posted a CAB which makes multiple registry changes. Also, see posts #2 and 3 for an alternate method that has worked for some.