Per Capita explanation...

Here's an explanation of per capita that you might use as a "spoken offertory" or in a newsletter or bulletin insert. It references some specifics for my church, but tweak those parts to reflect your own experiences. We posted signs all over the church that said "Got Per Capita?" and the amount for our church for this year for our presbytery giving (including the actual per capita assessment for GA). After several weeks, do this in worship:

Got Per Capita?
You’ve seen the signs...so what exactly is per capita and why are we talking about it today? 

Per capita is an amount of money per active adult member that congregations pay to the larger Presbyterian church. You might hear it referred to as a head tax, but it’s really better thought of as our gift to each other.

Per capita directly pays the bills for our General Assembly meetings, so that everyone who is asked to represent us at that meeting can participate regardless of distance or financial resources. But it does more than pay that bill.
Per capita helps us help each other do mission, ordain ministers, solve problems, support new congregations. The Young Adult Volunteer in Mission program and Jay Hankins and Allie Utley participated in is supported in part by per capita money.

You may be thinking that we don’t see much that happens with that money...not like we see the work of the dollars kept here at Forest HIlls and you might be right. Much of the denominational work and mission may not be visible to us at this moment. But this church exists because of the generous gifts other presbyterians provided when we beginning. The larger church provided us with ordained pastors, the larger church helped us organize, the larger church nurtured our faith so God could call us together as a congregation to serve here in this part of High Point. It’s like pitching in to pay for gas on a road trip with friends. You don’t see the gas, but it keeps the car moving forward and it gets us where God wants us to go.
The tradition of this church it to let you know what our per capita is for the year and encourage you to participate by giving that amount. Some members “pay it forward” and pay someone else’s per capita as well...just for fun...perhaps in honor of their connection or their influence on faith and life in this community.

We know the church of Jesus Christ extends far beyond our walls. Per capita is a way we enact the belief that we are part of a greater church, part of a greater purpose, part of things seen and unseen that we could not imagine or achieve on our own.

Thanks be to God.