Thanks everyone for your input. What I did and it worked great is...........
1) Created my artwork in Photoshop with the outerglow.
2) In FLexi I have the correct background color from a previous job for the same customer so I took the cmyk color chart, exported it as a postscript eps, opened it in Photshop, flattened it, saved it as tiff, brought it back in Flexi, Printed it, Matched background color on chart.
3) Added a background to the artwork in Photoshop (color matched from chart), flattened it, saved it as a tiff, took it back to Flexi, laid it on top of the 98"x650" (vector) background field, Did a eye dropper for back-up.
4) Masked off a section, printed it and it looks great.
Thanks isign and Mason, all our thinkers worked it out.