Start a project in your free time inside your office hours to show them they are wrong.
I can't see the point of doing work demos dressed as pet projects unless you have a performance bonus or significant equity at stake.
Even then following blindly their "dogma" will make you look better, at least in the short and medium term.
Besides, they may even sue you for IP violation if you use any of their data/code/business rules for your datasets/program.
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Edit
I haven't read well the "inside" bit in inside your office hours in parent's post so my first point is moot and scarface74's remarks are on point. Sorry for the misunderstanding.
Yes it is right. A few different things will happen.
- They will see the error of thier ways, change direction, invest in your side project and give you a nice little raise/promotion/bonus for it (not likely)
- They will see the value of your idea, use it in thier business and give you a nice little pat on the head. You can use that on your resume and get another job making more money.
- They will not like your idea, but you still learned a lot and you can still leverage that to make more money somewhere else based on what you have learned.
Unless I have some great way of monetizing a side project (which I never do), I’d much rather do a side project for my employer. I get to see it out in the wild, I have a defined goal based on a real world use case, and it keeps me more disciplined from taking shortcuts because I know it will be reviewed by others and I can get thier opinions - even my managers.