howto force libreoffice impress automated slideshow to recalculate embedded calc component on slide change?

The impress slideshow runs continuously and must show a number of days, compared to a reference date. If i don’t enter the embedded component interactively, impress doesn’t recaclulate the formula in the embedded object. How can i enforce, that on slide change this recalculation is done to show the correctly calculated value ?

i found on openoffice bugzilla ( an article that is quite similar.
when i alter the embedded CALC object to a DDE CALC object, and goto the “edit links” option in “impress”, the radio button to choose “update”, is greyed-out… and thus, also the DDE link does not update in my automated slide show.