This functionality is broken and will be fixed in Service Pack 1.
If your BIOS supports it, an updated I8042prt.sys will allow you enable this support by using Regedt32 to navigate to:
Double-click or Add Value name Headless, a REG_DWORD data type.
A data value of 1 will enable the hot plugging support.
You must shutdown and restart your computer for this change to take effect.