I've been trying to answer the same question, and so far the answer seems to be, "No." I did find this post from Ken Case in the OG mailing list, where he suggests drawing a line, setting the line type to orthogonal, and then adjusting the corner radius until you get the kind of arc you need:

http://www.omnigroup.com/mailman/arc...05/003607.html

Not sure if this addresses your need for specific degree measurements.