The easy, no-paint fix - but ... skill is required. Drill and tap the back of the head tube. Take a SS pan head screw and grind or better turn the head down to pump peg size. (Use one for e 3mm Allen, not 4mm.) Screw in. Done.

Years from now when it is paint time, back out that screw and have a framebuilder braze on a ball bearing. Locating hole is already there! My Peter Mooney got exactly that a couple of years ago when I had a very nice paint job done after braze-ons, minor 50k mile stuff ... by Dave Levy, Ti Cycles. Got the bike back and started building it up. "Shoot! I forgot the pump peg." Called Dave, not expecting what I wanted to hear but he said he could do what I just outlined. Cool! But, I'd have to leave the bike. Not for the time needed but for the proper headspace to locate the hole and drill and tap a round tube with beautiful paint and get it right.

I brought the bike in on a quiet morning. Dave was feeling it and did it while I waited. Perfect. Cost me a half hour of shop time, so an expensive drill and tap but well worth it.

Edit: The Mooney did not get a pump peg new because I was already an HP fan for life. And Zephal HPs didn't have frame fit pump handles. Also, that was one year after my head injury. Money was very tight. Peter Mooney was just starting out and his prices were unheard of low but still, I ordered the bike with just extras that were cost effective over say the next three years. (Cantilevers. $35 for braze-ons, $30 for Mafac calipers, $30 for very nice Mafac 2000 levers. Just cables and pads for the next 25k miles.) Oh, the Campy seatpin sucked with the brake housing hanger and several years later, my Peugeot UO-8 pin became available and went on for the next two decades. Almost 75k miles on that pin!