Okay, "can't" is too strong a word. But I don't know a good word for "it's technically possible but is cumbersome, is not idiomatic, and requires introducing another stack frame for no good reason".
With a given implementation or is there something in the Go specification that prevents this from being compiled away? If I were to write something similar in, say, C++ with a good compiler I would expect the generated code to be equivalent to using a ternary operator.