Yes, the input on the MG100 is on the back of the unit and the BD2's output is on the side, but I'm not sure I understand the question here. Angle connectors should work fine.
In your case, I would probably place the BD2 to the right of the expression pedal and run a 6" to 9" cable with right-angle connectors from the BD2 output to the MG100's input jack. For example, something like this should work fine:
http://www.guitarcenter.com/Livewir...Pack-Black-1337871391627.gc?pfm=item_page.rr1
I would use a regular straight connector guitar cable from the MG100 to the amp.
My guess is you will probably like the internal overdrive pedal of the MG100 enough that you won't need the BD2.
Word of caution: you may wish to leave the MG100's compressor off when using the BD2 in front of it. Compressors are usually best used before, not after, OD's. If you want the compressor on, you may wish to engage the MG100's noise gate to fight the probably noise resulting from OD before compressor.
And if pedals are new to you, unlike the front panel of an amp, which represents the signal path from left to right from input gain to pre-amp EQ to power amp output level, pedals and pedal boards tend to run the signal from right to left:
AMP: input gain -> preamp EQ -> output level
Pedal: output level <- EQ <- input gain
I hate to admit it took me years to figure out this right to left path, but it's important to understanding how to properly adjust your pedals. If you didn't know this, keep it in mind when adjusting your BD2. If you did, sorry for stating the obvious!