How do I to use a Pad transform with a constant value?

[vanossj]

I'm looking at the various pad transforms that end up using np.pad such as SpacialPad. I can set the mode="constant" but how do I provide the constant value to use? np.pad has a constant_values param but I don't see that getting set in SpacialPad

[rijobro]

See this issue and the corresponding PR to enable this functionality: #2460.