How can you build a floating two-port VCVS?
A difference amplifier, with a buffered virtual ground and unity gain is close to your VCVS.

Difference amps are often drawn with the output relative to ground (replace U2 below with ground).  But the output can be relative to any low impedance reference point.  Below I've added U2 to create a virtual ground, so that the output is Vx relative to U2's noninverting input.







simulate this circuit &ndash; Schematic created using CircuitLab

It's not perfect:


the input impedance is finite (could buffer though)
all the inputs have to stay within the PS rails and op amps' CM input ranges
input and output need to share a ground (it's floating but not isolated)
will need compensation if it oscillates.