I thought more about it and we should be fine with two functions (untested):

enum Skip {};
@property ref Skip skip() {
   static __gshared Skip result;
   return result;
}

void scatter(T, U...)(auto ref T source, ref U targets) {
   assert(source.length == targets.length);
   foreach (i, ref target; targets) {
       static if (is(typeof(target) != Skip)) {
           target = source[i];
       }
   }
}

void gather(T, U...)(ref T target, auto ref U sources) {
   assert(target.length == sources.length);
   foreach (i, source; sources) {
       static if (is(typeof(source) != Skip)) {
           target[i] = source;
       }
   }
}

Usage:

auto t = tuple(1, "hi", 2.3);
int a;
string b;
double c;
t.scatter(a, b, skip); // assigns a and b from tuple
b = "!";
++c;
t.gather(skip, b, c); // assigns tuple from variables b and c