I think you would have to use the Parametric EQ to copy the surround channel to one of the user channels, low-pass it, and add that to the left/right channel.
Then use Room Correction to high-pass the surround channels and discard low frequencies.
I'm not sure that you would get good results from it however.
You're probably better off just moving LFE to the front left/right channels and high-passing the surrounds without redirecting the low frequencies.
Thanks for your replies and I can see how what you suggested would work.
What I'm trying to do is the best way to output 4.0 with my L and R being large to handle LFE and my SL and SR being small with no LFE and I'd like to direct bass from them to the L and R. Although I can see as you point out, there might not be much difference/point to doing more then just removing bass from SL and SR. My digital interface is a Focusrite Scarlett 6i6 which is a 6 channel input USB device.
I've just upgraded from 2.0 to 4.0 speakers and this is a work in progress with getting JRiver settings how I want and how I think should be done. I need to point out that I don't want any up-mixing from let's say a 2.0 video soundtrack to 4.0.
I've had a bit of a play with the JRiver settings and it appears there are many ways to skin a cat, but I think what I've got works. I think the screen shots say many words. Regarding the second screen shot, that is the Room Correction setting for both SL and SR with all other channels untouched. Regarding the third screen shot, I've silenced both the Centre and Subwoofer because my digital interface takes 6 channels but I only have 4 speakers so I though it would be good practice; by the time they are silenced they should be mixed into L and R appropriately.
Suggestions welcome!