I may be struck dead for touching the ark of the covenant here, but I believe that it is wiser for a church to budget foreign missions giving rather than create a separate "Faith Promise" fund. On this eve of my church's annual budget meeting, I tried to listen to this sermon (only got about half-way through) from my pastor, Scot Shelburne, on which method is closer to the biblical model.
Our church had used the budget model for a long time, then switched to faith promise for a few years until we voted to switch back a year or so ago under the leadership of our pastor. He taught this sermon before we voted. I thought it might be interesting to some of you who may be thinking about the same issues. [Note: The link above is a direct link to the MP3 file. It would be a hassle for you to find it on our church site without the direct link.]