You can't as far as I am aware. You can specify the default location thats within Tools and Options but the attachments will appear on a seperate line and not in the subject line.. Thats a new on me, that you could ever do that..
OnePlus 5 review
Alice Saey's mesmerising animation for Dutch singer Mark Lotterman
iPad Pro 10.5in (2017) review
Comment booster votre iPhone ?