You can get an adapter for the top of the weber carb that adapts it to a standard air filter. There is one mid way down this page that goes to standard 5 1/8 :
http://www.carburetion.com/Weber/weberpartsair.asp
There is a variety of sizes at this page:
http://www.carburetion.com/Weber/adaptors2.htm
I forget which one fits the stock luv air cleaner, just have to measure the opening on it though. I am planning to do that myself eventually. I get really tired of listening to the sucking noise coming from the weber stock filter.