To begin with, I beleive you are looking for the 'centroid'. Otherwise, I'm not sure what the "center of an irregular shaped area" is.
Generally GIS applications are very much in tune with centroids, for example labels are typically anchored to the centroid of a closed area. You might have some luck with a field based GIS application.
In full AutoCAD:
Use the REGION command to convert the Polyline to a Region, then use the MASSPROP command to list its physical properties, which include the centroid.
I do not think I've come across anything in Carlson Survey or SurvCE relating to your need. Sorry.