To my knowledge this isn’t currently possible with Shader Graph. I know they’re working on adding support for more explicit render state settings for Shader Graph, but I’m not sure if I saw Alpha to Coverage as one of the options. For HDRP it doesn’t even necessarily make that much sense since that rendering path is more focused on deferred & TAA. The LWRP/UniversalRP is more focused on forward & MSAA, but there’s been no hints of any built in support for Alpha to Coverage or even render state settings.
Hopefully they’ll copy Unreal and automatically use Alpha to Coverage on shaders that use Alpha Threshold.