Drilling a stress relief hole might help on some frames, but on your blue frame, the crack's already all the way through the lug.
The blue middle section of the headtube is a separate tube bonded in. It should be safe from cracking, as the headset cup only fits into the lower silver cast section, which is cracked.
If you can find out which alloy the lug castings are made with, and de-bond the headtube, it would be possible to weld up the crack with the right filler rod.
Any welding around the headlug without separating the tubes will also kill any epoxy bonds in the area, making it even less rideable; only 80ºC needed.
If I understand ALANs correctly, unlike Vitus bonded frames, the tubes are threaded into the lugs and bonded so in order to separate the lower head lug you'd have to de-bond the DT/BB and TT/ST junctions too.
(Not sure if they are standard thread on both ends RH/RH, or RH/LH like turnbuckles.)
Then sand, clean, acetone and re-bond the top tube, down tube and headtube junctions simultaneously using a good quality structural epoxy, then hold the frame in a jig to keep the alignment while the glue sets.
IMHO probably not really worth it.
All the best,
Pause, take a breath and ask yourself: "What would Rastamouse