A few weeks ago I made a refugium area to me sump and it seems to be working. My sump is smaller - it holds about 23g and is very simply: raw water chamber, filter socks, skimmer section, baffles, return pump section. I divided the return pump section in two using the front part for a refugium. What I did was to get an inexpensive piece of corpalst, cut it to size and use it as a baffle. The waterflow through the refugium happens two ways. When I feed I turn off the retun pump and skimmer and the whole sump fills with water - when the pumps go on again the water level goes back to normal and there has been a full flush of the refugium. I also have my outlet hose from the GFO/Carbon reactor come into the top of the new refugium area.
It is far from perfect, but like you I didn't want to drain and take apart the sump - that didn't seem practicle.
