Ultimatum Game Deadline in Script

[Andrewbaine]

Is there a way to allow a certain redemption path before and only before a certain time/blockheight? CLTV causes paths to open in the future, I want to close them down.

For example, here's an imagined script that gives A and B until the end of the year to negotiate an agreement, after which the funds revert to C.

Code:

2017-01-01 OP_???
IF
  2 <pkA> <pkB> 2 CHECKMULTISIG
ELSE
  <pkC> CHECKSIG
ENDIF