In IC614, this is easier. Streaming out from virtual memory can be properly done from the GUI without needing to type in a command line, and there's also SKILL support. You can do:
Note the documentation for xstOutDoTranslate leaves a little to be desired - I've pushed for this to be fixed (I requested the ability to do this from SKILL, but it seems the documentation has not been done properly).
In IC613, you need to fill in the field on the form with the same command line arguments you would give to the strmout command from the command line. e.g. "strmout -help". You could enter:
strmout -library mylib -topCell mycell -strmFile mycell.gds
in the field.
There's no public SKILL function in IC613 to do the stream out from memory (you'll need to move to IC614 for that).