Variable Variables and Associative Array

Hi,
I'm trying to use variable variables with associative arrays,
but i can't quite get it right..

I know the below should not work, but I'm including it to help convey what I'm trying to do.

$Given_Tag="var1";
$$Given_Tag["DEFINED_VALUE"]=1;

Basically I want to end up with $var1"DEFINED_VALUE"]=1;

Cheers.

Have you found any answers?

This works and prints "hello".

$fred = "hello";
$var_name = 'fred';
echo $$var_name;

But this doesn't work...

$fred = array("item" => "hello");
$var_name = 'fred["item"]';
echo $$var_name;

or
echo ${$var_name};

Any suggestions?