I bought a pair of CAT safety boots last year and they took 4 Agonising weeks to break in. I found using lots (and lots) of fabric bandaid or similar while waring them eased my pain.I hate to say it but imo a good pair of work boots shouldn't need breaking in .
Dubbin is good for softening up the leather too!
2 pairs of socks and loads of vaseline. It'll take 2-3 weeks to break them in fully in my experience.