A 64-bit client is now available for use with the 4.3.2 PTR. You can download it at the link below, unzip it into your PTR directory, and then run the executable to test it.
The 64-bit client is being distributed separately from the PTR as it is not yet supported for use with World of Warcraft.This can only be used with the 4.3.2 PTR, it is not to be used with the live version of the game.The game’s built in voice chat does not currently work in the 64-bit client.[Mac] The 64-bit Mac client does not currently support the in-game movie recording functionality.[Mac] The 64-bit Mac client iTunes' Remote feature does not work at the present time.[Mac] The 64-bit Mac client does not currently support the customized LCD display for the Logitech G15 series of keyboards.[Mac] The 64-bit Mac client is currently not supported on 10.5 systems. You will need 10.6.8 or later for this version.Build 15211 - PC link, Mac link
If you encounter any issues while using the 64-bit version, please report your findings in the PTR bug report forum (http://us.battle.net/wow/en/forum/2359401/), and return to using the 32-bit executable.