RIght now? You do not. Sadly. THer are third Party tools for that, though. SOON: Use WIndows Server 2012 oR windows 8 - RDP is significantly improoved, including the ability to sense available bandwidth and for example even play videos over RDP, preferably with a graphics card on the server that is used for encoding. The keyword is RemoteFX. Helps to run virtual machines on a server you control so you can enable it. Sadly THat is still some months in the future, though with the release candidate out in 2 weeks time, I think I will make a test... get a new machine on the 8th that is not used for a month, only setup tests, so I will give it a try there
If the tablet RDP client supports it - you can configure to use 8-bit color, disable visual effects, disable audio passthrough, etc. which will help.
the biggest and easiest saving is to disable the background image and go all plain color. Not all RDP clients support this as a client setting, so do it on the server. Re bandwidth: an easy way is to use the Task Manager and look under the networking tab. On my 1900x1200 full color desktop I'm pulling about 8k/sec. You can cut that into 1/3 by carefully playing with the settings. Allan