speed change - exporting 24bit

Hi guys,
I’m using Audacity 2.0 (March 2012) with Windows 7 Pro.
I’m loading in a 48000/24bit file and changing the speed, when I go to export it the WAVE selections only allow 16 bit and the FLAC selection is also 16bit.
How do I keep the speed changed file at 24bits?

In the export dialog select “other compressed files” from the dropdown and then click on the Options button


Thanks heaps!