Yes, you can spray some (SuperThrive) on the kieke's roots & (undersides of) leaves... (Just don't get any into the crown) And DO NOT use it undiluted! (sorry to "yell" but u could burn the roots, & that would be very bad in your case) It only takes 2 drops (superthrive) per liter of water... If you want my opinion, I would say, (if you can,) get/order some seaweed extract. I use "KelpMax" brand, it's from Ray, & its a very good product (Dont know if Ray (
https://www.firstrays.com/cgi/cart/commerce.cgi ) would ship KelpMax to Mexico or not? But any other seaweed
extract, is good too, & usually you can find these at local, or online Hydroponic stores). KLN is also a good product. One thing to remember, you will wanna keep them (KLN/seaweed extract) in the refrigerator... they will degrade very quickly in heat/warmth, & light, so dark & cool will help them to last longer. **Another important thing to know about these root-growth hormones, is that you should only apply once every two weeks, otherwise, if used too often, they can actually inhibit root-growth. Trust me, I used to use it at every watering, when I first discovered it (& I didn't know better), & I saw nothing (& this was during the summer-time growth period) - and I got no roots whatsoever! (that was also w/ Superthrive). .....*Now, I apply once every two weeks, I use KelpMax and right now, I have an explosion of new roots; and extending, and side-branching older roots.
Good Luck! Also, to induce root-growth naturally, (and it helps to do this along with the rooting hormones), you'll want to provide warmth (85°F +/-), lots of humidity (80% +/- ...w/ some air movement... Don't want rot), and keep the medium on the dry side... I know that sounds wierd, but you want the orchid to think/know that it needs to grow roots, & they grow roots when they are thirsty (they don't need to be bone-dry, just barely moist). Also, too much moisture in the medium may rot what little roots they have left. The dry-ish medium is why u need the higher humidity - you don't want them to desiccate any further by losing even more water from their leaves, than can be taken in by their roots, the high humidity will help to slow water loss. Good Luck! I hope you can get this guy to pull through! Holler back if ya have anymore questions!
About the kieke paste, I'm not sure it would induce root-growth... I say this, b/c I have noticed on the online stores, that in addition to kieke paste, often the store will have a "root-growth" paste as well (which is intended/needed to go along w/ the kieke paste
$$). So if that's the case, I would assume the kieke paste doesn't induce roots.... But, I could be wrong
Dont have Keikei paste, should I apply Superthrive?
... it's currently drying off... should I apply the fert and hormones tomorrow, or just plain water?
Also, if you can, cut out the bad parts on this 'chid that are rotting, use a sterile blade, and sterilize the blade before using on anything else (preferably sterilize btwn each new cut, but if not, that's probably ok). And, one more very important thing, DO NOT apply cinnamon to roots (only on the cut ends) it will desiccate the roots (which is why it's good for cuts, it dries it so it won't get infected, but not for the whole length of a healthy root) I made this mistake, the first time, and it killed the plant, b/c it didn't have many roots to start, & I poured cinn. all over it's roots! If you have done this, it's ok, just grab a soft-bristled toothbrush, and run the roots under luke-warm tap water, and scrub *very gently* until it washes off. 
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