No weapon like this exists canonically, and it would likely be difficult to build given that lightwhips usually have many smaller lightsaber crystals, rather than the one (sometimes two or three) large crystal used by a lightsaber. They also lack the cell barriers necessary to keep the blade contained in a straight line. Theoretically, I believe you could create a weapon capable of turning those barriers on and off, but I can’t see it having a particularly stable blade. If it works for you, it would be exponentially easier to have a hilt (standard length) with emitters at both ends, one for the lightwhip and one for a regular blade, that the wielder could choose from. Naturally, they couldn’t both be used at the same time, but it is a simpler solution.
I hope that helps!
~ Jacen
Write Better Star Wars 