For single angles, the steel design parameter LPA can be used to account to eccentricity of applied distributed loads. See information from the Help Context explaining this parameter:
This option only applies to angle sections that are designed with respect to the geometric axis and not the principal axis. The section needs to be defined with the box "Laterally Restrained for Torsion" checked. The torsion force is considered in the design of the member only. When reviewing the analysis forces, the torsion force will be 0.
Otherwise, using a series of point torsional moments as you suggest is one way to account for the torsion. You could also use short, rigid members (length equal to the eccentricity) that cantilever from the member to account for this effect.