Ways to get 2 + 1 tuners working?

[Shrikey]

I've got mine set up with S/C tuners and while everything is working nicely, the missus is not happy.
When I record something, now and then happens that she would like to watch something else on a channel that is not in the same channel bundle (whats it called in english?) and thus not possible to view.

What I'd need now is a way to add a second cable tuner, so that I'd have 2 cable tuners and 1 satellite tuner available.

I know its not physically possible to add a third tuner into the machine, but are there ways to circumvent this?
Additional external loop through tuner?
A single twintuner card (are there such things)?

I know I could do something with 500-series box over network (harddisc shares and so on), but seems to me a bit too expensive way to resolve this problem. Unless I can use the tuners over network too.

Ideas or is it simply impossible?