Segmentation based on variable equivalency without discreetly identified values

I NEED to be able to build segments that don't require discreetly defined variable values, but can be based on var1=var2.

Any easy example would be this:

[Visit bucket [entry pagename]=[exit pagename] AND [path length] >1

Another, more difficult example:

Show me all eVar1 values that have both mobile phone and tablet instances.