I've often thought about this, but never done it, and this thread was the inspiration. I improvised a set of strings from my string drawer, using one new string and three used and put them on my Warwick Corvette FL:
130 - a fifth string from a new set of Sadowsky flats. The taper core is so long that it wasn't really compatible with my 5-string. The "B" sits perfectly in the saddle of the 'wick and taking it up a half step helps with the flop factor;
90 - an old Fender 9050; feels perfect;
70 - an old Fender 9050; a bit tight;
45 - an old TI Jazz flat; I've always found these to be of too low tension, so it makes it up to A just fine.
Since the D is a bit tight, I'll probably dig up a 65 and put it on tomorrow. Other than that, it's a new challenge that I'm looking forward to. And I now have a set of Sadowsky flats for 4-string that I can use elsewhere.