I use an x10 shutter switch which is a relay which switches the power to the up and down motors for a set period of time when commanded.
The commands come from an x10 module which sends signals round the mains wires of your house.
You can buy an x10 command module which gets it's signals from an RF remote, or an IR remote, or a timer, or speech recognition, or from a computer, or from a phone receiver etc.
Obviously the cheapest options are RF and IR.
The RF command modules tend to plug into the mains like one of those timer switches and the IR ones are just a box which plugs in like an appliance.
The shutter switch is a bit like a light switch and has to be wired in the wall in a similar way.
It can be found for £40 plus vat and delivery (£53.46)
here or it's called a motor drive switch and costs £43.20 from
here.
There is a great plug and play starter kit for about £30 from
here which gives you an rf remote, a receiver/commander/plug-in modue and a lamp module.
This allows you to switch your lamp on and off as well as an appliance (or appliances using a multiway socket extension - mine switches the power to my pj and subwoofer) and also another two x10 modules eg the shutter switch for the screen.
If you need any more info just ask.
Cheers,
Cal.