[plt-scheme] read line from drscheme input port

I am writing a DrScheme tool which occasionally needs to get a line of
input from the user. I would like to call (read-line
<drscheme-input-port>), where <drscheme-input-port> is the default
active port in the DrScheme REPL (as opposed to stdin). How do I
access that port, or how else can I tell DrScheme to graphically
prompt the user to enter a line of text?

--
Aleks Bromfield
abromfie at cs.brown.edu