Most probably, what you want to do is that the Arp drives the synth, not viceversa.
Said that, Psycle does not accept transmiting midi messages between the machines, there's only midi from psycle to the plugins.
In that sense, there's no way to make the Arp drive a synth in current Psycle implementation.
It would need some other way to redirect these messages, which I haven't thought about.
<[JAZ]> Pa pi pa pa pa pi pa.... ;ĚD