I’m replying to myself, in case anyone else runs into this issue.
The simpler way was to simply create a new noise variable and add it to the
real and fake images before calling:

input.data.resize_(real_cpu.size()).copy_(real_cpu)
additive_noise.data.resize_(real_cpu.size()).normal_(0, std)
input.data.add_(additive_noise.data)
output = netD(input)