Specifying eponymous template "internal parameter"

[monarch_dodra]

Sometimes (especially in phobos), one defines a parametrized 
template, that resolves to a templated function.

This is a nifty trick, because it allows specifying a vararg 
before the current type parameter, eg:

//----
auto r = [1, 2, 3];
auto m = map!("++a", "--a")(r);
//----

As you can see, the template guessed the type of r, even though 
we used a vararg. This would not have worked with a single 
template function.

My question though: I have a similar use case, but I NEED to be 
able to explicitly specify the type of r: as such:

//----
auto m = fun!("++a", "--a", ubyte)(1);
auto m = fun!("++a", "--a")!(ubyte)(1);
auto m = fun!("++a", "--a").fun!ubyte(1);
//----
None of them work. In this specific case, I *need* to specify 
that 1 is of type ubyte, but I really can't do it :/

Simplified example: in my use case, it is a "immutable(int[])": 
Failure to specify the type means the compiler strips tail 
immutability...

The only workaround I can find to make such a thing, is to *not* 
use eponymous temples, and explicitly call an inner function. 
This is ugly as sin, and it makes specifying the internal 
parameter mandatory.

Any thoughts?