As far as I know, this does not exist. See e.g. my request from 2009 viewtopic.php?f=4&t=725&p=3009#p3009
I'm forced to copy whatever I want to replace with, and then press "find next" and "paste" a lot. Obviously this doesn't work for regular expression replaces, which I'm forced to do all at once or by clicking the replace button with the mouse.
I would really love for this command to exist.
On the plus side, four out of the five things I requested were implemented. Just not this one.