Combine mono buffers into single stereo buffer

I feel like I'm missing something obvious, but I haven't figured out a good way to do this. I want to be able to combine 2 mono buffers into a single stereo buffer. I'd also like the process to be automatic, rather than use record~ and build it in real time. I built a patch that splits a stereo buffer into left and right channels, and then converts them into mid and side channels, and now I'd like to be able to recombine them back into stereo.* I thought maybe using assigning a peek~ object for each channel of a corresponding stereo buffer, but the result is still mono. It's likely I'm doing something wrong though.

*I want to use this with a fluid.bufnmf~ patch, which only outputs mono files. If you load a stereo file and set it to decompose it into 4 components, you actually get 8 files, 4 for each channel. So I thought I'd try running the mid and side separately and then recombine those into stereo. I'm pretty sure I could use fluid.bufcompose~, but I'm wondering if there's a native Max way to do this.

edit: ok yeah, fluid.bufcompose~ is the simplest way.