You just force them. With the STR 19 belt from the Adventurer's Mart you can force a huge number of locked doors and containers, and with Draw Upon Holy Might (either the spell or the Bhaalspawn ability) you can force most of the rest. 18/51 is all you need to finish the paladin quests.
Personally though I rarely do "pure" solo runs, though, because I like to complete all the NPC quests (and because you can't enter the Planar Sphere on a pure solo run without being a douchebag). So when I've got Yoshimo for Renal's quest, I usually make sure to pick any of the extra-hard locks in Athkatla that contain good loot but can't be forced. With an effective "pick locks" of 80 at STR 25, though, there are only a couple.
Thanks, All the times I have played through this game, I never realized you could do that.