Well, no, anyone can't actually - I certainly have tried and failed numerous times !
One can convert any audio file to MP3 format using Sound Forge Pro 11. I use this programm to clean up audio files, but it can also be used as a converter. If one wants a freeware programm, there are several of them. A quick search on the Internet finds these : Format Factory, Free Mp3 Wma Converter, MediaCoder, Switch Sound Format Converter, GX::Transcoder.
Possible answer, as on some 'blogs' which make downloads available, is to give the option of both 'flac' & 'mp3'.
This is actually a good solution too. Avaxhome users often do this. Uploading the CD or LP in two formats : one lossy and one lossless. That seems fine to me.