Struct Flattening

[dsimcha]

I'm working on porting dstats to ranges and I've run across an interesting
problem.  I've defined a range that I'm going to use for joint entropy, etc.
It's basically a tuple with some special properties.  Let's say I have a
template struct:

struct Joint(T...) {
   T ranges;
}

It's built with:

SomeType joint(T...)(T args) { // do stuff. }

When one of the arguments is a Joint, I want it to flatten.  For example,

Joint!(uint[], uint[]) r1;
uint[] r2;
auto result = joint(r1, r2);
// result is a Joint!(uint[], uint[], uint[]), not a
// Joint!(Joint!(uint[], uint[]), uint[]).

Is there an easy metaprogramming trick that I've overlooked to make stuff
flatten like this?