The answer was simpler than I thought it would be. Credit to [John B][1], one can use a sub-shell `(...)` for this:

 ➜ time (sleep $(sleep 3; echo 1))
 ( sleep $(sleep 3; echo 1); ) 0.00s user 0.00s system 0% cpu 4.007 total


 [1]: http://stackoverflow.com/a/21820530/1916449