line integration of scalar field for use in study, not as result

hello,

i am having great difficulty figuring out how to use a line integral inside of a study. for example, i am seeking to use the line integral of a temperature field (1st interface) across a line in order to find an avg. temperature across that line and then use this value to apply a volume force to fluid flow (2nd interface), as in natural convection. i can find the line integral in the results section, and am trying understand how to employ this sort of function in the study itself.

any help here would be greatly appreciated,

thanks,

henry