If you wire the tweeter to a separate connector you can biamp it. Does the cabinet have a passive crossover in it? If not, it's pretty simple. Just hook the + terminal of one speaker to the + of the jack, the - terminal of the speaker goes to the + terminal of the other speaker, the - terminal of that speaker goes to the - terminal of the jack. Done.
HTML Code:
Jack
+ -
| |________________
| |
| ___ |
+ - + -
Speaker Speaker
The impedence will then be 4x what it originally was, though. ie, if it was 4 ohms (2x8 in parallel) it will now be 16 (2x8 in series).