simulate VGA on HERC using BGI driver

[SRGXNBS at grace.dsir.govt.nz]

I've got a cad program I use at work which requires EGA/VGA, I'd also
like to run it at home but only have a herc screen. The program uses
a BGI driver .. I was wondering if it would be possible to "fake" VGA
by writing an EGA/VGA simulation .BGI driver for a hercules screen? It
would also require a pop-up facility to adjust the colour->monochrome
translation on the fly. Most cad (electrical) is 2D anyway so I should
be able to operate the program (EAGLE by CadSoft) ok.
Any help/comments etc. appreciated ....
bruce