Prx1 seems to be a very promising target for height increase as it seems to have targets early in development.  Unfortunately, I couldn’t find any Prx1 stimulating substances but hopefully you can?  Srx1 is involved in the repair of Prx1 so that could be another target as well.

Regulatory divergence modifies limb length between mammals

“Natural selection acts on variation within populations, resulting in modified organ morphology, physiology, and ultimately the formation of new species. Although variation in orthologous proteins can contribute to these modifications, differences in DNA sequences regulating gene expression may be a primary source of variation. We replaced a limb-specific transcriptional enhancer of the mouse Prx1 locus with the orthologous sequence from a bat. Prx1 expression directed by the bat enhancer results in elevated transcript levels in developing forelimb bones and forelimbs that are significantly longer than controls because of endochondral bone formation alterations. Surprisingly, deletion of the mouse Prx1 limb enhancer results in normal forelimb length and Prx1 expression, revealing regulatory redundancy. These findings suggest that mutations accumulating in pre-existing noncoding regulatory sequences within a population are a source of variation for the evolution of morphological differences between species and that cis-regulatory redundancy may facilitate accumulation of such mutations.”

“One developmental control gene known to promote limb skeletal elongation is Prx1, also called MHox or Prrx1. Prx1 is a paired-related homeobox gene expressed in somites, craniofacial mesenchyme, and limb mesoderm during mouse development”

“the forelimbs of Prx1BatE/BatE mutants are on average ∼6% longer than their wild-type littermates at E18.5 ”

“The forelimbs of Prx1-null homozygotes are ∼12.5% shorter than controls at E18.5”

“average mutant long bones express ∼70% more Prx1 than wild-type siblings”

“Long bone chondrocyte proliferation is elevated by ∼6% at E15.5 in Prx1BatE/BatE mutants.”

“[The Prx1 induced] limb elongation arises at stages of mouse gestation when Prx1 expression is limited to the perichondrium of the developing limb skeletal elements. It is known that the perichondrium is an important regulator of endochondrial bone growth”<-Could this be related to the zone of Ranvier which should be connected to the perichondrium?  Since the zone of Ranvier is linked to an earlier developmental state of the growth plate it could mean that Prx1 could be helpful in inducing neo growth plates.

According to this grant, Prx1 inhibits bone formation so it favors an earlier developmental state overall.