Two ways using the same concept (and included Sonar tools).
1) This is more mastering (so after you've mixed and exported). Import your mixed export to a new "mastering" project. Clone the track. On both tracks insert the Sonitus Multiband (compressor). On the first track enable every band except the lowest band (so all the low frequencies are silenced. On the second track do the reverse (mute all bands except the lowest frequency band). Now on the second track (which is only playing back the low freqs) hit the Stereo Interleave button to turn it into mono. Of course you may want to adjust exactly how wide that low band is so if you want to adjust it do the adjustment then clone it to the other track. That way you can mute the necessary bands without having any frequncies ommitted or duplicated (because you cloned the effect the band settings will be identical on both instances).
2) If you want to do this IN the mix then do essentially the same thing but with Sends and Busses. So make sure ALL your tracks get sent to two busses right before the master (so you would be routing your subgroup busses to these if you are using them. Otherwise you'd have to set it up on every track. You shoudl always use sub busses though for instrument groups). So on all your sub busses set the output to one of your Sonitus Multiband busses and create a Send to the second Multiband bus. Then you just set your frequency bands as described before and set the Interleave button on the low freq bus to Mono.
Of course you need to set up all instances of the Sonitus Multiband to not do ANYTHING to the signal. So no compression or limiting or whatever. You are just using it as a frequency splitter.
That is kind of a bastardization/reimagining of some Anderton techniques.
Cheers.