It won't work because the 3impact engine is a standalone exe. They do not provide any source so you can not modify it. 3impact is slow and just sucks. A much better physics engine that can do collisions with boxes and arbitrary shapes, and not only spheres like 3impact, is ODE at http://opende.sourceforge.net - and it's free.
This engine was recently made compatible with Blitz3D. You can go to blitzbasic.com to check it out. Apparently it needed a userlibrary installed in the userlibrary folder and then the Tomahakdll.dll needs to be in the same folder as your executable. The physics engine is free for both commercial and non-commercial use.