[Groff] Graph Spanning Columns

[Paul O'Leary McCann]

I'm writing a paper in two-column format, but I have one large graph
(generated with grap) with a caption that I'd like to span both columns.
I was originally using the ms macros and I assumed that by using a
display with BD I could get what I wanted, but I couldn't get it
working. 

The best I've got so far is like this:

.BD
.1C
#graph & caption
.2C
.DE

But this causes an immediate break and leaves the rest of that column
blank.

Using KS/KE causes the document to superimpose a lot of text on that
page. 

I also tried using mm's non-breaking 1C and keeps, but these resulted in
either another empty column or text printing over part of the graph. 

What is the proper way to get a graph to span two columns in a document?
-POLM