Push two symbols to stack at once in a push down automata I am pretty new to PDAs and I was solving a problem which asked to design a PDA for the following: $a^n b^{2n}$.

The transitions on the PDAs I've encountered so far have pushed only one symbol onto the stack at any time. Can we push two symbols?
Eg: for every $a$ I encounter I push two symbols.  Thus, the transition will be:

$\Delta(q_0, a,0;000) \to \Delta(q_0)$ 

where "$a,0;000$" indicates pushing two zeroes onto stack for every $a$ that it encounters.
There are some options (from comments):

By some definition of PDA, you can push a string $w \in \Gamma^\ast$, where $\Gamma$ is the stack alphabet. (from abc's comment)
Even if you could push only one symbol per transition, you could modify your PDA to push the first -&gt; move to a new state -&gt; push the second -&gt; continue as usual. (from chi's comment)
The third option is to use multiple stack symbols encoding different things. (from Raphael's comment)