perhaps the biggest question after a low preshot number is, will you be around to monitor him and do you have supplies to handle any low numbers that come your way?
have you read the "how to handle low numbers" sticky at the top of the lantus page? basically you want to be gathering information during this phase to tell you how clyde is responding to lantus. you want enough data to tell you when he usually drops during the cycle and how fast, and what the low point might be. in other words, as much as possible you want to be able to predict what he will do after the shot.
at some point everyone has to learn to shoot lower numbers. don't do it until you have that information above and are ready to monitor him. the path to lowering their BG numbers, and subsequently the dose, includes shooting lower numbers.
until you have the data to predict, you can either 1) wait a little bit for the numbers to rise to a number you are comfortable shooting (say 15-30 minutes and retest) without giving any food - that's important - don't feed while you are stalling; 2) you can give a partial shot or 3) you can skip the shot.
probably your best bet if you are confronted with a lower-than-normal preshot BG is going to be to post here and in your subject line ask for help making that decision. don't feed while you're waiting. if no one is around to walk you through it, read the sticky on low numbers and make the best decision you can.