restrict alias this?

[Namespace]

Based on my previous thread 
(http://forum.dlang.org/thread/rpcqefmyqigftxsgs...@forum.dlang.org), 
I got the question whether it is possible to restrict "alias 
this"?
Similar to templates function, e.g. "void foo(T)(T value) if 
(isNumeric!(T) ...", but it should be limited here so that it 
does not interact with the cast or something other.
As far as I know, "alias this" is an implicit cast. And just like 
an explicit cast (opCast) it should be possible to restrict it.

Otherwise, I have unfortunately run out of ideas how I can allow 
an implicit conversion.