[Phanx]

Oh, I misunderstood what you wanted to do... I thought you actually wanted to open the tradeskill window for a specific profession. For what you're trying to do, I couldn't find a good way to toggle the spellbook from insecure code in ~10 minutes of testing, so you're probably going to have to do one of those out-of-combat workarounds:

local clicker
local function HideClicker()
          if not clicker then return end
          clicker:ClearAllPoints()
          clicker:Hide()
end

dataobj.OnEnter = function(self)
     if InCombatLockdown() then return end

     if not clicker then
          clicker = CreateFrame("Button", nil, UIParent, "SecureActionButtonTemplate")
          clicker:RegisterForClicks("AnyUp")
          clicker:SetAttribute("type", "macro")
          clicker:SetAttribute("macrotext", "/click [btn:3] SpellbookMicroButton")
          clicker:RegisterEvent("PLAYER_REGEN_DISABLED")
          clicker:SetScript("OnEvent", HideClicker)
          clicker:SetScript("OnLeave", HideClicker)
          self:HookScript("OnHide", HideClicker)
     end

     clicker:ClearAllPoints()
     clicker:SetAllPoints(self)
     clicker:SetFrameStrata("DIALOG")
     clicker:Show()
end

dataobj.OnLeave = HideClicker

Note that this will also hijack your tooltip, so if you need a tooltip, you'll have to set OnEnter/OnLeave scripts on the clicker to show/hide a tooltip. If you want to do other things on left/right click, you'll have to modify the clicker's macrotext attribute.