Yep, just keep changing what your doing on your off days. 3 days together like that will always take a toll though, and I think the reason you have plateaued is because you can't really fit more in because of work.
I can only suggest that if you can do a workout on the 2nd 'work day' of 30mins, and replace the 2nd 'off/cycling day' with a recovery ride (while upping the 1st and 3rd day off intensity or distance) you might get a little extra out of yourself.
30mins isn't much, but it is enough to get some good quality high intensity training in. 10 or so mins warmup, 10-15mins warmdown. Then take your choice of super hard intervals to fill in the middle 10mins
Probably the hardest, but most beneficial, is two 1min efforts at almost 'kilo effort' intensity. They will warp your mind with pain, but they build lactate power like no other training method.
Do the 2nd one after 5mins break from the first. Don't do them at absolute 100% effort. Your looking at an effort intensity that has you lactating up hard at about 45secs into the first effort, and about 30 seconds into the 2nd. But if your cracking hard in the 2nd effort at say 20secs in, stop at 45secs and warmdown. And you must do the 15min warmdown... its just as important as the effort in this form of training.
The other workout you can also try three 2min on/2min off efforts as race winning intervals. i.e. Hard 5-10s sprint, then hold form and keep the power going hardcore, but slowly releasing the effort over the next 2mins, aiming to only lactate up right near the end of each effort.
When you get good at pacing the 2min efforts, you will learn how to get to 1m45s with a little in the tank such that you can then do an all out sprint of 15seconds.
Other than that, I don't think you can get much more out without looking for another job, sorry :/