By the rule, no heavy fortification on bracers.
I wouldn't allow it.
However, I would allow a monk to use a shield without losing his abilities like he would for armor (a good argument can be made either way on that), and then he could have heavy fortification. If your DM won't allow that, you might be able to get armor-type enchanments (not including enhancement bonuses) on your monk's outfit, though that is a very generous house rule for sure.
You can find some discussion of pros and cons of allowing monks to freely use shields in my Guide - click on the link below.