If you just don't like referring to the global %-, maybe something like:

s/$regex/transform(%-)/ge
sub transform {
   my %matches = @_;
   ...
}
[download]

Or you can do a second match.

s/($regex)/transform($1)/ge
sub transform {
   local $_ = shift;
   if (/^(\[\[($http)]\[($title)]])/) { return transform_named($2,$3) 
+}
   elsif (/^($http)/) { return transform_http($1) }
   ...
}
[download]

Or you might use something like this.

while (1) {
   if (/\G($named)/gc) { print transform_named($1) }
   elsif (/\G($http)/gc) { print transform_http($1) }
   ...
   elsif (/\G(.)/gcs) { print $1 }
   else { last }
}
[download]