May I ask why? Worried about the pitcher getting hurt?
I have to agree. Although there are many different ways to cover on bunts, it is certainly not unusual for the pitcher to cover 3rd with runner on 1st if the 3rd baseman ends up fielding the bunt. In fact, a quick google search of "bunt coverage runner on 1st" yielded validation of this. Here are the first three links I looked at...
Basic Bunt Coverage #1: Runner at 1st « Coach5150's Baseball & Softball Blog
Softball: bunt defense situations, bunt defense, second baseman
Girls Fastpitch Softball: Intermediate Bunt Defense
All of them agree that with a runner on first that whoever doesn't field the ball between the pitcher and 3rd baseman is to cover 3rd.