Consider using VMware Virtual Desktop Manager (VDM 2). This product uses a secure HTTPS connection between the client device and the VDM 2 Connection Servers. This ensures that all traffic from the client device, including the RDP connection, is secure. It is encrypted within the HTTPS connection.
VDM 2 also has several other security features designed for use in a VDI environment.
Please refer to the document http://www.vmware.com/pdf/vdm20_intro.pdf for more details. There is also a VDM 2 specific community here.
Mark.