Personally I couldn't live with it when there is a solution, but it's your call of course.
While you don't need to pick rogue at level 1, you could get deleveled to before martial weapon prof feat (amia player tools > characters, to see when you grabbed it in case you don't remember) and snatch a rogue level (unless you picked it at level 1, then you need to make a new character or ask for a rebuild).
-IF- you grabbed the feats in the same order you mention below...
"Taken so far...
Weapon Finesse
Expertise
Extend Spell
Martial
Weapon focus shortsword"
...you'd just have to drop to level 8 (1 xp from 9) and grab rogue at 9 for weapon focus: shortsword.