how encourage cats onto cat-bed ?

Some of you might have been through this process before and might be
able to save me a learning curve.

Our two cats are very affectionate and although we leave them a warm
living-room to sleep in at night, they nearly always follow us upstairs
to a chilly bedroom at bedtime. As you may all have experienced, cats
don't bed down and sleep eight hours solidly. Their comings and goings
across the duvet at various points in the night, do not a good night's
sleep give - for the humans!

We have just purchased an electric blanket specially manufactured for
cats. Some of you will know what I mean. It's essentially just like an
ordinary electric blanket except that the heating cables are protected
within a stiff vinyl "pillow-case" and the electric supply line is
encased in a strong thick cable that can't be chewed through. The vinyl
blanket comes in a soft furry pillow-case, which can be easily slipped
off for occasional washing.

We are hoping the cats will take to this blanket. There's room for two
of them on it. It's 16" x 24" and our cats often sleep side by side.

So the question is: how do we get them to choose the warm electric
blanket (on top of a thick and soft rug) down in the living-room instead
of spending the night on top of our duvet in a chilly room?

Please don't say, "Shut the door and just trap them in there!". That
would be too easy. And cruel. We would prefer them to continue to have
access to all parts of the house, including the bedrooms.

So it's a question of how to get them to choose the cat-blanket.

Thanks.

Eddy.