It was a real design,read the NASA report;
The second broad variant of the Pegasus approach (under investigation by
de Havilland of Canada) is to augment the thrust of the forward nozzles by using ejectors located in
the fuselage (Fig. 4). This has the advantage of retaining the cold front exhausts (thus a voiding the adverse effects of hot gas ingestion) and providing a relatively low impingement velocity on the ground plane. The two rear hot nozzles are again combined into a single nozzle as in the previous discussion.
Uncertainties that remain to be resolved include (a) the extent to which thrust can be improved
by cold flow augmentation within the geometrical constraints of a practical supersonic aircraft
design, and (b) the effect of the fountain caused by the impingement of exhaust flows (in this
case heating effects should not be a problem due to extensive use of cold air; however, the
fountain may cause upset moments on the wing and fuselage).
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19820002156_1982002156.pdf
