The Keep Mateo Situation

I am enjoying reading everyone's projections on how the pitching staff might shake out this season.

Many posters would like to see Juan Mateo pitch his way out of Single A and into St. Louis. I wouldn't be against that; it would be great having an actual power arm out of the pen.

But what if he doesn't quite blow the doors off Roger Dean yet shows enough to make the decision difficult? If I'm not mistaken, we can arrange a trade with the Cubs to send Mateo to the minors.

My question: Whom would you trade to keep Mateo?