Transparent Blend by Shader Variant in Surface Shader

Hi,

Ive written a large multi compile surface shader using shader_feature for various features (normal, spec, emission, vertex color, rimlight etc) (much like U5s standard shader but surface instead of V&F). I would like to be able to control transparent blending by a shader_feature but cant find a way to do this in a surface shader.

Am I correct in saying that transparent blending can only be achieved by the #pragma surface parameter "alpha:blend" and this cant be enabled or disabled by shader_feature? Or is there another way to achieve this that I have overlooked?

Thanks in advance