Push two symbols to stack at once in a push down automata
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)