A commenter over at Volokh Conspiracy who identifies himself as an anesthesiologist links to this web page for a product for injecting drugs into the bone:

What is EZ-IO?

The EZ-IO® Intraosseous Infusion system is a complete solution for immediate vascular access in all patients larger than 3 kg. Used an estimated 160,000 times across the world the EZ-IO® is the leading choice for intraosseous access in all care environments from the ambulance to the hospital to battlefield and beyond, the EZ-IO® system is designed to help the medical professional gain vascular access in seconds to provide intravenous therapy to patients. EZ to use, EZ to train and EZ to maintain the EZ-IO® is the clear choice of intraosseous solution for medical professionals and the best method to gain immediate vascular access...when you need it most.

The commenter says it is "relatively painless." Doesn't sound like it to me, but I don't pretend to know anything about it.

Oh, and I am reasonably certain that everyone on death row is "larger than 3kg."