Delphi MVP and my friend Simon Stuart just updated his MonkeyMixer utility for XE5 (in addition to XE2, XE3 and XE4).
Once installed (and you’ll need to close the IDE before installing, by the way) you’ll be able to right-click on any VCL or FMX project in the Project Manager to toggle the project between VCL and FMX.
You do this by clicking Switch Project to FireMonkey or Switch Project to VCL(depending on what the project type is at that time).
Download the latest version. (Updated for XE6)
Keep in mind mixing FireMonkey and VCL forms in the same application isn’t officially supported, but this is a good option for migrating a VCL application to FireMonkey, or just including exactly the features you need.