May be useful for other modders. There are some mods already that introduce own attach tools but they, in fact, work as usual KIS tools which is not fun.

Can be done by extending ModuleKISItem.ItemAttachMode with new value and introducing an extra field to specify names of allowed tools.

As far as I know this was already done and it worked in 1.0.5 for the Hammer tool from ExtraplanetaryLaunchpads. The survey stakes allowed to attach themselves to the ground only via hammer.

Hammer in EL has just a slightly different set of flags but in any other means it's a usual KIS attachment tool.

toolPartAttach = true
toolStaticAttach = true
toolPartStack = false