The only way I have managed to control the wild wind changes you experience with the default real world weather download option in FS9 is to use Activesky,I don't have a registered copy of FSUIPC,but even so using the freeware version and ASKY I do not get those ridiculous wind shifts and consequent rapid drops/increases in air speed that the default weather engine seems to produce,however much as i like ASKY and use it most of the time I do like the speed and simplicity of the default fs9 weather when I wanted a quick hit for an equally quick flight.
PS I also tried FSMetar(freeware) but using that program did not stop the wild wind changes(presumably as FSMetar seems to be a metar down loader only and still uses the default weather engine to process the weather info).At this moment ASKY seems to be the only option if you don't want your 747 landing on its back occasionally or your Cessna doing impromptu barrel rolls/loops etc from time to time :D
Andy
PS I did manage to find a freeware download (AVSIM/FScom)of many more weather themes to add to the default FS9 themes which are a good substitute if a quick flt is on the boards.The themes don't seem to suffer from wild wind problems.