What I do is to initially enter the Mean Wind (available on the CFP) for the entire flight, after entering that the time and fuel at destination are quite reasonable (good for the passengers in-flight display also).
Old Smokey, do you have a reference that defines precisely what Boeing means by "Enter the forecast cruise wind" for CRZ WIND? I used to do what you just described (mean wind on CFP) but was told off by an "I'm never wrong" CPT who said it should be the initial cruise wind.
Thanks
P