It's something that isn't well represented on the tabletop, so I had a few ideas about how to implement such things:
- Polearms with hidden blades allow you to switch from a reach weapon to a close-combat dagger as a Free Action (instead of a Free Action to drop the weapon, and a move action to draw another one). Useful for swarms of small enemies who can get right on top of you.
- Maces (I'd also allow clubs, greatclubs, morningstars and most other blunt weapons) with blades hidden within the handle allow you to switch from Blunt/Bashing damage to Slashing damage as a free action once per encounter - useful if you get swallowed whole by some huge beastie and need to cut your way out. Should you roll a Critical Failure in combat, causing you to lose or damage your weapon, you can negate the failure by switching to the other weapon (though the attack is still considered a miss).