Actually you can already trigger Arp steps using a Sync Delay with a negative value to produce the required amounts of Clock messages at your leisure. 
(6 clock messages is equivalent to a 16th note)
Stepped ARP.mhp (415 Bytes)
This preset is triggered by the Middle C key (note 60), note on & off messages, but you may adapt the first line to trigger on whatever you’d like to, it should simply make sure to send a Start message into the Sync Delay pipe.
The 2nd line simply drops the Middle C note out of the stream, so it won’t interfere with the ARP pipe.
The Arp is set up in a way that it reacts to your trigger notes lengths.
Send a Start message directly to the Arp pipe to resync it, so that the next trigger signal is the one that plays a note.
Maybe this somewhat achieves what you’re after ? 