How can I significantly increase my credit score using cash?

I would like to improve my credit score^ by throwing money at it rather than by waiting several more years for a ding to disappear from it.

I’ve read several good questions and answers here about using cash (e.g. with a secured credit card) to increase one’s credit score, but I haven’t seen any discussion about the limitations of such an approach.

1) Is the credit utilization component of the credit score purely a ratio as described in this article, or is any attention paid to the absolute dollar amount of unused credit?

2) If the answer to (1) is that it’s purely a ratio, then how far from 0% utilization can I be before my credit score loses points? U=5%? U=1%?

3) Suppose the answer to (2) is 1%, such that if U=1.0% I lose P points, but if U=0.9% I lose nothing. Then suppose that I typically put $1000 onto my credit cards each month and that my total credit limit across all cards is $10K. So currently my U=10%. Can I simply go to a bank and open a secured credit card on $91K collateral? That would bring my U down to

1,000 / 101,000 = 0.99%

and maximize the utilization portion of my score.

Now, Googling yields this survey from 2011 that indicates $30K was by far the upper limit for a secured credit card then. Other websites seem to agree that $10K is about the best I could do nowadays.

4) Why do such limits exist? Since I have to pony up the collateral in advance, why can’t I get any credit limit I want? What is the risk that the financial institution fears?

5) Assuming that those limits for secured credit cards are real and non-negotiable, is there another form of fully-collateralized credit that I can establish with a financial institution and is reported to credit bureaus as a revolving loan? How about as an installment loan? Given that there’s such a thing as a home equity line of credit, and a home is (literally) infinitely harder to turn into dollars than cash is, shouldn’t I be able to establish a cash line of credit just as easily? Are there any institutions known for a willingness to custom-build products like these for clients?

^ For the purposes of this question, by credit score I simply mean the “typical” or “average” FICO-style score.