1. UNICOM is the name for a ground station, and the question said there was no UNICOM.

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2. The closest ATC unit would be at another airport, and could be hundreds of miles away.

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3. You address the traffic as, for example, "Powell River Traffic, this is ...."

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4. You are talking to all the traffic, not just the guys you hear. It's okay to address a call to a particular aircraft, if you want to clarify the pilot's intentions. You can address it by any portion of the call sign you remember, or by another means, "Zulu Victor Papa, this is Zulu X-Ray Tango: can we go ahead?" "Aircraft calling east of the river, say your altitude" "Last aircraft calling, your transmission was unreadable."