Mmmm...
Can't see an easy solution to that. My first thought was a Client/Server solution where the user downloads from a certified ANSP (Air Navigation Service Provider) such as UK AIS and then submits the data to your site for processing and you then present him with the output. However I can see that this would cause a problem with threading and increased traffic levels at your end. (Please be aware that I am no programmer).
Perhaps we need to wait for the legislation to develope before we can look at ways of working within its strictures.
Alternatively maybe you could work with an ANSP who would cover the certification requirments in exchange for your traffic bringing some benefit to them. I think this is the thinking behind Avbrief's tie-ups with both Navbox and Notam Plot. I'm sure Avbrief make no profit from acting as the data source but they may get some benefit by association, i.e. it brings their products to the notice of potential customers.
The alternative of course is that a commercial provider just nicks your ideas in order to provide a paid for service, which would be a poor reward for all of your hard work.
Mike