I don't know if it's possible to train the corpus callosum, but aside from that, I don't think you can read text in the left visual field for longer than a fraction of a second.
To be able to read or see something in your left visual field, your eyes must be focused on something to the right of that (Imagine a fixation cross in the middle of a PC screen where your eyes are focused on and a word appearing to the left of that). First of all, you will have the reflex doing a saccade towards that word, so your eyes will be focused on that word and the word will be in both visual half fields.
Even if you can suppress that reflex, the word will not be projected onto the fovea, so the vision will not be sharp. The word will be blurry if it hasn't a huge font. If it has a huge font, there's a possibility that part of the word will be in the right visual field as well, because it is so big.
I think reading one word this way is rather difficult, I cannot imagine reading a whole text this way. Certainly because a whole text exists of multiple lines, which will be blurry and perhaps difficult to distinguish. A whole text is also wider than one word, which would be or presented partially in both visual half fields again, or even more to the left, where the vision would be even blurrier.
If you assume that you can read a text this way, I don't think it is possible to have more fibers, but it might be possible that you will have thicker fibers, or at least stronger connections between hemispheres, which could result in a shorter interhemispheric transmission time. The brain is pretty plastic. Who knows.
Please note that all of this isn't scientific, but more or less my opinion.