Passive is simply not that difficult to identify. If you can't tell passive from active, you lack grammar skills in several areas, which means a trick like this really isn't going to help. You should even have to think about passive. If you have the needed grammar skills, if you understand simple sentence construction, you should write active without even thinking about it.
For that matter, just reading novels and short stories should make writing active automatic. There are times when passive is the right choice for something, but I have to stop, think a minute or two, turn the sentence over in my head two or three times, and then try to write passive.
As Buffy says, the problem is not understanding good sentence construction. A write who struggles with passive does so because he doesn't know how to construct sentences properly. This means he's going to have awkward sentences everywhere, even when active/passive isn't involved. I see this in slush piles constantly.
Tricks won't help you. Avoiding to be verbs completely won't help you, and leads to forced writing. The only thing that can really help is learning what good sentence construction is, and how construction make a sentence active or passive.
The bonus is that you'll also stop writing poorly constructed sentences everywhere else.