You can create a custom lens that includes those sites and point a custom bang at it.
For example I have a custom QT lens that only includes results from [*.qt.io, *.stackoverflow.com, *.github.com...] and a !qt bang pointing to it at https://kagi.com/search?q=%s&l=8
(you'll have to change the l= id to point at your lens)
Comments
You can create a custom lens that includes those sites and point a custom bang at it.
For example I have a custom QT lens that only includes results from [*.qt.io, *.stackoverflow.com, *.github.com...] and a !qt bang pointing to it at https://kagi.com/search?q=%s&l=8
(you'll have to change the l= id to point at your lens)