Would need a QB79 (or QB78D /2078) barrel and a new .22 bolt. Be nice to get a spare set of seals as well, seeing as you're going to be inside of things anyway.
Archer's spart parts list the QB79 .22 barrel as currently out of stock...and he doesn't sell just the bolt. Does sell a QB78 caliber conversion kit (that includes a bult), but the barrel on the QB78 is thinnner than the QB79...would have barrel band issues.
So...there currently isn't an easy way.