LTMOM - Fixed value like accounting date

Hello,

I'm trying to use LTMOM and to have some variables. With LSMW, it was easy to add a variable, and during convert phase, user fixes the value and we move into the variable. It's simple and for example, field like accounting date, it's perfect.

In LTMOM, how can we declare variable that the user will fixed during the conversion/preparation phase ?

Philippe