Do you have any idea how to get by bus from Split Central bus station to Stanići (a small village near Omiš).
It's quite easy, fortunately!
Stanici is on the the Adriatic Main Road, and as you say, quite close - 5km from Omis.
This is conveniently between Split and Makarska.
If you just go to the general bus terminal in Split, there is a local bus service to Omis every half an hour. However, you can actually use any city bus service between Split and Imotski, Makarska or Dubrovnik, as they stop in Stanici on the way.
Double-check before you buy a ticket, but that was the common way when I was there.