How to start up xmonad with apps on other workspaces

I'm trying to write an xmonad.hs which, at startup, launches some apps on some workspaces. Several of these apps (e.g., atop) will run within a terminal (urxvt being my preference).

This has been asked a few times before, e.g, here, here, and is obliquely touched on on the XMonad FAQ.

However, these rely on:

1. using spawnOn from XMonad.Actions.SpawnOn, which flat doesn't work (testing with urxvt, and also xclock as a simple example); it gets sent to the current workspace.

2. using spawn prog >> windows $ greedyView <workspace>, which kinda works, but has major timing issues - e.g., if you run two in succession, with different workspaces, both progs end up on the latter workspace. FWIW, I experimented with using threaddelay to assist; it didn't make any discernable difference, even with a 10s delay between spawns (I remembered that threadDelay is in microseconds, and so used 10000000).

3. rely on using general hooks for programs - meaning that whenever I start them up, they'll get sent to the given workspace. That's not what I want; I just want them placed there at startup.

Relatedly, it surprises me that the API doesn't let me start up an app and then give me a reference to that app/window (potentially with a timeout); so that I can confidently send that app/window to a workspace.

Any help would be greatly appreciated.