We calculate optical forces on dye-enriched resonant nano-shells in dual-beam Optical Tweezers. We investigate the non-linear gain-assisted enhancement of their optomechanics and study their behaviour through Brownian dynamics simulations. When the wavelength is red detuned with respect to the plasmon resonance, we observe that the particles are efficiently trapped at the laser beam intensity maxima of the dual beam standing wave. Conversely, for blue-detuned wavelengths the nano-shells are channelled through the standing wave antinodes due to the sign reversal of the optical force. This open perspectives for gain-assisted optomechanics where non-linear optical forces are finely tuned to manipulate controlled nano-photonic systems.