...

Can I compare one attribute at a time versus all of the others combined?

Yes, you can use the Compute biomarkers task which will perform Student's t-Tests on the selected attribute, by comparing task to compare one subgroup at a time to all of the others combined; by default, the up-regulated features (e.g. genes) are reported as biomarkers. An alternative option is to set up the differential analysis model comparison is this way; for more information please see the information here for each model. 

...