I don't believe coin-control works properly yet - with GSC transmissions, however sending a Diary entry with coin control and Send "may" work, but I haven't specifically tested that (that is only good for HEALING anyway).

But to answer your question, 'exec sendgscc' gives you some control.  It skips over locked coins and sancs.  It does consolidate all applicable coins into one transaction - coins whose coin-age adds up to the "pog_coinagepercentage=.nn" percentage.  So if you set that at .50, it would keep adding inputs that are not locked until half of your coin_age is accumulated in the transaction.