Hmm riding slower in the fat burning zone only really works for decent length rides doesn't it? If your only doing 5miles each way just blast it and get a decent CV workout. Do longer rides at night or weekends. If you cant spare the time for that much riding do runs instead. Chuck in any other exercise you can, sit ups and press ups need no equipment and you can do anytime.
Other than that sort out your diet
While your trying to lose weight
No biscuits/cakes EVER
No Alchohol AT ALL
No fried food, grill all meat and stick to chicken/fish.
Only have semi or skimmed milk
Cut out most if not all calorific drinks (coke, tea, coffee etc)
Drink lots of water, helps make you feel full and you burn calories easier.
Go hungry, it won't kill you, don't starve yourself but give yourselve a normal portion (which may not be what you think is normal) then don't go back for seconds.
Now me I'm a glutton, I eat like a pig but I do enough excercise to keep weight off, 100miles+ per week - thats just to keep from gaining weight not losing weight - but I used the above a few years ago to lose 2 stone and do similar after christmas/holidays where I've eaten loads but not been able to excercise.
It's hard work but it's mainly mental, get your head sorted and the rest isnt that bad especially if your chosen method of exercise is fun (mountain biking) and it's well worth it.