According to the post from a member from Chiphell forums, spotted by Videocardz.com, while you can't enable those 4096 stream processors on the RX Vega 56, flashing it with the RX Vega 64 BIOS will change both the GPU and memory clock frequency, significantly improving performance.
As you know, the Radeon RX Vega 56 comes with 3584 Stream Processors, down from 4096 SPs on the RX Vega 64, as well as features lower GPU and memory clocks. The RX Vega 64 BIOS has 1545MHz GPU Boost clock while HBM2 works at 945MHz, which is somewhat higher than 1471MHz for the GPU Boost and 800MHz for HBM2 on the RX Vega 56.
With this minor clock boost, the RX Vega 56 actually ended up only two percent slower compared to the reference RX Vega 64. By further overclocking the RX Vega 56 to 1650MHz GPU and 2200MHZ memory clocks, allows it to actually outperform the reference Radeon RX Vega 65, showing that it is not all about a number of Stream Processors.
As is the case with overclocking, this BIOS mod will depend on the actual sample as it could happen that all RX Vega 56 cards simply can't achieve such clocks. The BIOS mod also voids the warranty, but should not be a big problem since all current RX Vega graphics cards actually have two BIOS settings.