[ICOM] 706 MKII - CW filter on SSB

[Buck]

I have a stock 706 MKII.  It does not have any additional filters installed
in the two places to install them.  However, I find that receiving an SSB in
CWR mode, I can filter out most of the surrounding noise.  On SSB mode, the
signals are wider and pick up much more QRM.  I can't talk SSB from CW mode
and setting up the split is too much work for most of my QSOs.  

Is there a way to fake the radio out to think that the CW filter it uses can
be used for SSB?

IF they are the same filter (I only see one, the original and two open slots
for add-ons), how does it get a narrower bandwidth in CW?

Thanks in advance
Buck
N4PGW