We too get a corporate discount, and at first glance, fares seem very attractive. But I've always had huge problems with these corporate leisure tickets - they are very inflexible, earn low miles (in fact, I can never even get my DC card attached to the booking - it seems to default to some dummy DC card number), and there never seems to be availability (e.g. business takes from the I award fare bucket) - so I have always reverted to buying normal fares...
The other issue is that the very lowest fares displayed I think now *do* require a Saturday night stay... I think the "generic" T&Cs are incorrect (I'm sure you used to be able to buy one ways, but I think it's changed recently). I tried a dummy booking for LBA-GLA, and got this in the fare conditions box:
Originally Posted by bmi website
travel from last stopover must commence no earlier than the first sun after departure from fare origin
Sorry, but I think unless you stay a Saturday, I don't think these specific fares are valid, and pre-travel support isn't going to be able to help