This paper proposes a low-cost workload distribution technique for the compute-intensive simulation of electron waves propagating in graphene superlattices, by fully exploiting the compute resources of heterogeneous GPUs concurrently. As old GPUs start failing and new ones are launched in the market, we equip our labs with more recent hardware, creating a variety of distinct GPU families that have non-negligent processing power available, but sometimes unused. Here we show how to exploit them with reduced parallel programming effort of the workload distribution on heterogeneous multi-GPU systems. The speedups obtained when comparing execution against uniform workload distribution (i.e. the same workload on each GPU) range from 1.2x up to 1.8x.