'Squawk **** and pass message'
...is something that we get here. There have been a number of on-the-ground face-to-face conversations about it, but the habit persists. I know it's a peeve of one of our (very experienced) FIs.
I suspect controllers do it (hopefully a controller will be passing along here soon) when they have a fair amount of traffic, are offering a Traffic or "Basic plus" service to someone and want to identify you quickly. From my perspective (low hours pilot) it chucks a bit of a spanner in the works in that it breaks the expected flow and puts a small spike into workload.
Response Options include:
a) "Squawk ****, standby" and then pass your message when you're ready
b) provide the litany and "forget" to read back the squawk on which case the controller should ask you once again to "squawk ****"
c) Write it down, look out, set the transponder, look out/pass the message and tag the squawk onto the end.
There is a short delay in a squawk code appearing on a controller's screen so any delay you introduce is just a part of the bigger picture that LARS providers see.