I've seen it done, though with one engine mounted under the belly of the plane. Rocket engines don't produce a ton of thrust anyway (A D engine will propel my 11oz rocket to about 100 ft) so I doubt you are going to rip the wings off or send your plane into an uncontrollable death dive. Keep the power reasonable for your first attempts (such as A motors) so you can get a feel of what your plane will do, then slowly increase the power.

Before youtry this in the air, rig everything up with igniters and make sure they will fire relatively close together. I don't think the ejection charge will adversly affect the performance, but you'll have to experiment.

"It is not because things are difficult that we do not dare; it is because we do not dare, that they are difficult."
-Anonymous