Since Alfonso helps so much, I thought I'd respond to help him!
 
You could import the functional connectivity Fisher-transformed R-values at the group difference locus as a second-level covariate.  If you only wanted to look at the relationship between functional connectivity and disease severity in the patients, you would need to assign [0] values in this second-level group difference locus covariate, such that the only data retained are those for patients [i.e., 0 0 0 0 0 0 0 0 -0.393 0.229 -0.24 etc].  Add another second-level covariate for the disease severity scores for just the patients [i.e., 0 0 0 0 0 0 0 0 2 1 3 4 etc.].
 
Once you have your two covariates, one for the connectivity in the patients at the group difference locus and the other for patient disease severity, you would go into Tools:Calculator and select the following:
 
Patients, Disease Severity  (as predictors)
[0 1]
 
and select the connectivity covariate as the outcome
 
This should show you the relationship between disease severity and connectivity in that group difference locus in the patients alone.
 
Hope this helps,
Jeff