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If you're not comfortable with that, you might consider using AdWords Editor to filter keywords weekly according to performance buckets (example: Under target CPA & not in top positions, Over target CPA, Way over target CPA). Then adjust bids in bulk by a percentage, according to bucket. Depending on the size of your campaigns you may need to do this more/less frequently.
None of this is as granular as running off of actual revenue per click, but it's a decent alternative if you don't have the budget for a tool.