What are known methods of non-surgically disabling neural tracts/pathways (esp. Corpus Callosum)?
I was able to find one non-invasive method to sever the corpus callosum (callosotomy). This method is referred to as gamma knife radiosurgery (Mathew et al., 2007). Basically, 201 beams of gamma beams are focused on the corpus callosum and where the beams intersect, the energy is high enough to permanently damage the tissue. I doubt this technique is available for routine use in animals, though.     

Another interesting technique is photothrombosis. This method is based on the systemic injection of a photosensitive dye named Rose bengal. Subsequent focal illumination of the brain with a cold light source through the intact skull leads to focal cortical infarcts of reproducible size, location and geometry (Schroeter et al., 2002) . Brain damage is induced due to photo-activation of the dye and subsequent endothelial damage with platelet activation and thrombosis, resulting in local blood flow interruption. The light source can be applied on the intact skull with no need of craniotomy, which allows targeting of any cortical area of interest in a reproducible and non-invasive way (Labat-Gest &amp; Tomasi, 2013). However, although the light source penetrates the skull, I don't think the method is useful for the induction of deep-brain lesions, as I was able to locate only studies using it to model cortical lesions.  

Having not answered the question, I'd like to say that either surgical sectioning, or chemical ablation using micro-injection of neurotoxins are the most commonly encountered methods to perform a callosotomy.

References
- Labat-Gest &amp; Tomasi, J Vis Exp (2013); 76: 50370
- Schroeter et al., J Neurosci Methods (2002); 117(1): 43–9
- Mathew et al., J Neurosurgery: Pediatrics (2007); 106(4): 312-5