You've not mentioned what your 'special effects' are, but generally this sort of thing is provided with a shader, which, as we know, isn't available in DX7 and therefore not available in Blitz3D natively.
If a shader could be used this would bypass this probably as you'd do the whole shebang in one render.
If a shader could be used this would bypass this probably as you'd do the whole shebang in one render.