Consider giving the following a try, it's an excerpt from Chapter 4 (Poly Block) from my eBook on the Heilx. I use Helix a lot to do pseudo-Nashville tuning. One day it hit me that the only reason the two top strings of a 12-string are doubled is because of physical limitations. So, I wanted to come up with something that had the vibe of a 12-string, but also, had some of the octave-higher top two strings mixed in subtly. The green text has no special significance, it just refers to other presets included with the book. The Poly Capo is transposed up an octave. Hope this helps!
Gourmet 12-String
The Gourmet12-String preset (fig. 4.13) wraps processors around the Poly Capo to produce a rich, bright, big 12-string sound for stereo or mono. It’s optimized for the bridge pickup, but other pickup positions work too.
This is based on the LayeredNashville preset. However, the sound is more like one guitar than layered guitars, because the second EQ (Low/High Shelf) doesn’t emphasize the highs as much. Also, to give a 12-string’s characteristic shimmer, the Dual Delay toward the output adds subtle modulation.
The crucial difference is the Simple Delay that precedes the Poly Capo. With a physical 12-string, there’s a slight delay (around 20-25 ms) between hitting the main string and its associated octave string. The Simple Delay emulates this effect. Your ears identify this as part of a 12-string’s characteristic sound.
Figure 4.13 For a synthetic 12-string sound from a digital effects processor, this preset comes very close.
For live performance, only some blocks are suitable for footswitching. All the blocks before the Mixer are essential parts of the 12-string sound. The post-Mixer Delay and Reverb are good candidates for footswitching. One (or both) compressors can also benefit from footswitching. Then you can call up sounds that are more or less compressed.