I believe the connector track was to follow the old CLAREMONT subdivision. This abandoned line diverges from the NEC just a bit South of Frederick Avenue, and heads EAST for about 1/2 mile, then curving Southeast crossing Wilkens Avenue on a high old trestle. Originally, the line connected with the SB B&O line via a curving connector that hugged a cliff while riding parrallel to the old WM Tide sub, but this grade has largely been lost since. However, CSX still serves one or two customers in the business park, so a newer connection is available that leads into Claremont Yard, near where I-95 goes over DeSoto Road.
The maintenance yards were to have been near Washington and Monroe, and MTA apparently bought the property in preparation for it. Today, it is little changed, though some of the open space has been used for storage of retired buses.
Another, much less direct possibilty would be to restore the connection to the old WM Tide sub north of the West Baltimore Station to the West, and follow this route under the B&O and into Westport where the Tidewater sub merges with the Curtis Bay sub, where a direction change would then be needed to back into Camden usng the Curtis Bay Sub and finally the mainline.
More info on the Claremont...