Give 5% of the block reward to the new PoW. This is enough to create a new DRAM-based mining community + hardware/software infrastructure without alienating/bankrupting existing SHA2 miners.
If SHA2 miners continue misbehaving (blocking Segwit, threatening to use other implementations), we increase the new PoW's reward with another soft fork. Hopefully this option won't have to be used: the threat will be enough to keep them compliant.
I like the sound of that implementation. It squashes a significant argument against a PoW change, avoids a hard fork, and would keep the markets far calmer.