No. The specs of the camera say SD or SDHC. I have seen Canon message boards with people asking the same question and they said there is no compatibility for SDXC nor is there a firmware upgrade to make the T1i compatible with SDXC.
However, there is belief that you may be able to format an SDXC on a computer and then use it in the camera, although this may work, it is not supported by Canon.