Yes, I did it twice, but the last time was four years ago. At that time HAL charged 110% of whatever the currently-being-offered price was for a "K" inside cabin or an "F" outside cabin, for what they called their "single shared" program. They would attempt to match you with someone of the same gender AND approximate age, and if they did not, you got the cabin to yourself. I opted for inside both times; the first time I was paired with a woman 5 years younger than myself, and we wound up in a "C" outside. The second time I was not matched, so had the cabin to myself, but it stayed an inside.
Unfortunately about 2 years ago HAL changed the deal so that the whole thing is now based on the BROCHURE prices, which means that it is no longer a bargain.
Interestingly enough, on my last HAL cruise I stopped by the future cruise desk to check on whether I could book a cabin and specify my partner at a later date. At the time I was interested in a transatlantic being advertised at $899 inside. The agent suggested the single-shared instead, and said I was wrong about the pricing, that it would be based on K instead of N and would therefore be $949 (plus the extra 10%). Wrote it up for me and said the receipt would be delivered to my cabin. Which it was, the next day, with a sticky note on it saying the agent had been reading the wrong line on her computer; the tab was now $2884 ! Discounting for taxes and port fees, that is what it would have been based on the brochure price, just like I thought. Needless to say, I expressed my displeasure rather forcefully.
To wrap up the story: I was interested in that cruise because a couple months earlier a TA had sent out a "package" offer that included it, but which sold out in just 2 days. But shortly after I got home from the one above, the TA sent a note saying he had been given 20 more cabins; I quickly contacted someone I'd exchanged notes with here on Cruisemates, and we snabbled one. Turns out that through them, the base price of an inside would have been $799, and outside is $894.