That is going to be difficult to do.
I can think of a couple ways it *might* be able to be done via JavaScript and image on load or similar. However I think it would be an awful user experience because it would have to essentially save and reload the record in the middle of them working. Not great and will likely be more frustrating to your users than the small chance of losing work. They will have to deal with that every day.
I think that for the most part you do not see many people talking about this because a power loss or some other issue is only going to affect a single record for most users. Yes some work is lost but it isn't like you are losing the days work or anything like that, unless your form is huge.
How big are the forms your users are filling out? Would it make sense at all to break them into smaller forms? If it is very large and takes a lot of time to fill out you could split it into several forms. That way when data loss did happen it would only be a small portion of the form.
Sorry that I do not have a good answer for you here. Maybe someone else will chime in with some other ideas.