Existing studies on the CO-OFDM optical networks are mostly based on the assumption that all the sub-bands of a lightpath are continuous in spectrum and transmitted on the same route. For better network capacity utilization, we apply Virtual Concatenation (VCAT) technique to the frequency domain by transmitting the sub-bands of a CO-OFDM optical channel via different routes. Simulation results show that the VCAT technique can significantly improve lightpath blocking performance and the improvement is more significant under a smaller VCAT sub-band granularity.