Really you have to pick between the two 'evils'.
1) Create only what you need, and when you need more use CreateFrame (it's not THAT bad, if it really scares you then check out IrielVirtualFrames from
http://www.vigilance-committee.org/wow/downloads/)
2) Create ahead of time enough rows to fill your window to the point it needs to scroll, then all you have to do is map your actual rows to the real ones (this is the usual 'FauxScrollFrame' approach taken by much of the standard UI)