No, you generally cannot use SD as SRAM; you can hold data there that you read out and print.
Click Additional Options, Browse to your sketch, and Attach it so other can offer suggestions. Might come down to needing a uC with more SRAM, such as the 16K that a '1284P offers, or the 8K in a Mega2560.
Here's a Duemilanove-style '1284P board I sell.
http://www.crossroadsfencing.com/BobuinoRev17/
