Unfortunately, the only valid shading control options for use with the Radiance daylighting measure are (interior) blinds, shade, and "switchable glazing", the latter of which is generally used for modeling electrochromic glass.
You could actually use the switchable glazing option to crudely model the effect of external blinds. The switchable glazing option swaps out two constructions, so you could make a construction with an improved SHGC and reduced VLT to swap in for the times the external blind is deployed. You'd obviously need to figure out what the appropriate values would be, and the "no-blinds" construction would also have to have an improved SHGC since the blind structure would introduce some shading even with the slats opened, but it's something. I'm not recommending this method, I'm just sayin' it's an option. YMMV, etc... ¯_(ツ)_/¯