AutoDesk Smoke :: Grab 1 Frame Inside CFX Schematic

In cfx, i have a source clip which i want to grab just 1 frame of it. So what is the best way to do it in term of efficiency ?

If i'm in timeline editing outside cfx then i can use alt-E and drag the clip to have a 1 frame copy. It's cool but how to do the same thing inside cfx ? i want to do it inside cfx schematic. Actually I can use a timewarp node or mux or maybe there's some other node that can do the same function. But is it gonna affect the speed of the whole tree ?

i'm comparing the two scenarios :
1. i did 1 frame grab in the editing then bring it into cfx
2. i bring the full source clip inside cfx and apply timewarp to get 1 frame to work with.

Is there gonna be different in speed ? if only single clip , i won't see any different. What i want to know : what is happening internally ? does the second scenario will eat up more processing ? If yes, then we need to feature to extract 1 frame inside cfx (just like in editing).

As an addition, in media bin, when i'm in editing module (outside cfx) , i can ctrl-E (cursor change to red icon) to grab 1 frame . But when i go to cfx then it won't work. ctrl-E in media bin won't do anything. It will be great to have that feature in cfx.