While I don't have an answer for you, I would like to ask you why you would use that strategy. I understand a potential tight budget and trying to keep costs low. Does your conversion and ROI work best from a 4-9 ad rank position? Your CTR's will be low, your QS will be potentially diminishing, you won't be able to gain from Ad Extensions.
I think you might benefit from the latest video that came out about Adwords Auction and might make you rethink your strategy ( if budget is the issue).
Insights on the AdWords Auction (only 8 minutes long)
Obviously lowering your bids will keep you down, and in my opinion eventually OUT....
Hello Dmitry P,
As Eric G wrote, there is no easy way to do this as in activating a software option. Partially it can be done through customized automated rules but at a high volume of impressions the system always shows some impressions to the top even if the majority are on the RHS.
If you use the Segment "Top vs Other" in the keywords tab, you can see that there are some impressions to the top even for keywords with the lowest avg. pos. if those received a few hundred impressions.
What you can do :
You can create daily pairs of automated rules for those keywords that can run at 3 hours intervals.
One rule can raise the bid by 3% for the requirements:
a) if the avg. pos metric is lower than let's say 5.5 and
b) if the impressions are at least 3, by looking at today's data
The other rule can lower the bid by 3% or more if the avg. pos. metric is higher than 4.0 and the same impressions are at least 3, using data from the same day.
For more advanced users, there is this script :
Sample conditions for the rule to raise bids