Increasing the caps as Farhan pointed out elsewhere would fine but then you should adjust the BFO
to put the signals in the passband. That mod however makes SSB really poor both RX and TX.
While I've not done this on a bitx because to me its primary SSB radio. I have made CW filters
for tests using that technique. A good example of this however is Kitsandparts 1W, the crystal
filter is optimized for CW and works well.
If one were really wishing to experiment replacing the caps with a smaller value and then putting
Varicap at each point results in an adjustable bandwidth filter [look up Jones Filter]. I've played
with this and it does work well. It was applied in the Elecraft K2 receiver as a working example.