I think that publishing new attr is the only way, please check my comment below:
To specify valid Data Partition constraint you need to specify:
1. On the left side - valid, related to current object, attribute that exist in schema. You can check all attrs using bop_sinfo tool. Example: bop_sinfo -a pcat
2. On the right side should be value OR list of values that matches attr's type. The only way to sepcify a variable is to use user referenced values. Data Partition uses: @root.<attr>, Scoreboard Query uses: @cnt.<attr>. Sorry for the typo I made in my prev messages, you need to use @root reference, not @cnt.