As "Blazin" said regular and frequent oil changes will keep the engine from sludging up. Other than tearing the engine down I would suggest just getting in there with a putty knife and start scraping. Try to keep the crud from falling down your return oil holes, might use an OLD shop vac to help while you scrape. you probably wont get it all but its better than nothing.
While you're at it you really should drop the pan cuzz its full of sludge to, clean it out and buy a new oil pump pick up, the screen is most likely plugged.
The problem with doing this is that you might just start circulating a bunch of grit that was embedded in the sludge and could cause problems with your bearings. I would use some detergent 5w30 oil and run it for 10 min. then change out the oil and filter, maybe you will wash some of the grit out. I remember my dad saying that some guys used to use diesel fuel or even kerosene instead of oil to flush the crankcase, only run the engine a minute or so, just enough to circulate the juices. Sounds kinda scary to me. I hope someone else has a better plan.