Post-flight update for future reference:

When going through the TSA Precheck line at BWI, I didn't see any TSA agents around to declare the formula prior to screening, so I kept it in my bag. The bag went through without any additional screening (with 40 oz of liquid formula).

When going through the TSA Precheck line at IAH, the bag was taken off the belt for additional screening, where each bottle of liquid formula was screened (but remained sealed).