You can get Beast to use IBL under the custom XML settings. This link
will let you know about most of the hidden lightmapping settings available when you use the custom XML settings. The only downside is that there is no visible skydome of your HDR image nor a widget or setting to change the rotation other than manually offsetting the image in Photoshop.
I would also highly recommend using the 2nd integrator Path Tracer that's mentioned at the bottom of this document. It has sped up my bakes by a huge margin and I have yet to find a downside to using it.