Hello,
Unfortunately this variable has its limits. You can't attach a function to its end. The only option for you is to use a user variable, i.e. bu_lpricedat_UV, where UV is the name of the user variable, but user variables cannot be set individually for each selection. That is, if you are only interested in, let's say, the favourite, you can add a trigger that will set the user variable BPMINUS1 to r_ticks(backprice,-1) for the favourite, and repeat this action "no more often than once in 0.3 sec". The in the other trigger you can get the values of these:
bu_lpricedat_BPMINUS1
bu_lpricedat_BPMINUS1
bu_lpricedat_BPMINUS1