I don't believe you can do what you're asking -- the BR1 is a cellular modem, the only thing it can do is send/receive cellular data and convert it to Wifi. If has no repeater functionality at all.
The Weboost is a repeater and can do what you want, but as you said, it won't give you the same MIMO performance as you'd get from the Peplink.
I'm not aware of any MIMO capable repeaters (and I'm not even sure it'd be possible to build one). Your best bet for fast data performance is to buy a data plan for the Peplink.
