x-exec://programname/foo/bar/baz?blort
is a very poor choice for URL syntax. I'm hoping that the initial "//"
will be used by URL schemes to denote DNS A-record fully qualified
domain names. (E.g., so that, if you know that mtv.com is now known as
adam-curry.org, you can uniformly modify URLs scheme://mtv.com/ to
point at the new host name.)
In this particular case, there is absolutely no reason to use //.
How about just
x-exec:progname;foo;bar;baz