What instructions are you reading?  IRS conveniently dodges this issue, as far as I can tell.  It's the same as "return of capital" dividends in Box 3 of the 1099-DIV.  The taxpayer is trusted to keep a running total of these and reduce basis when the stock is sold.  (I think some of the brokers do this for them, but I'm not sure.)  The problem with both "return of capital" and "liquidation distributions" is that they can accumulate over several years.  

I don't think IRS looks for LD's anywhere on the return, and I wouldn't put it on Form 8949 until substantially all of the proceeds had been collected.