8.0 Update: Still generally works, see comments
This addon, along with the LFGjoin addon, automates the tedium of creating and joining groups for shared lockouts when mount farming on your alt army.

It creates a macro that creates a custom group in LFG with a predetermined name.

1 Download and install the addon

2 Make a macro that says "/lfglist AAA"  (Replace AAA with anything)

3 Use macro.

4 Your group will be created!  

Works in tandem with the LFGjoin addon, which looks up the group you created with 1 click.

AutoAccept is NOT clicked, as most mount farming methods don't use AutoAccept.  If you DO want AutoAccept to be turned on every time, replace the entire LFGlist.lua with this:

local frame
SLASH_LFGLIST1 = "/lfglist"
SlashCmdList["LFGLIST"] = function(msg)
if not msg or msg:trim():len()==0 then
print("You need to provide a name for the group to form one.")
return
end
if not GroupFinderFrame:IsVisible() then
PVEFrame_ShowFrame("GroupFinderFrame")
end
GroupFinderFrameGroupButton4:Click()
C_Timer.After(0.25,function()
LFGListCategorySelection_SelectCategory(LFGListFrame.CategorySelection,6,0)
LFGListFrame.CategorySelection.StartGroupButton:Click()
LFGListFrame.EntryCreation.Name:SetText(msg:trim())
C_Timer.After(0.25,function()
LFGListFrame.EntryCreation.ListGroupButton:Click()
frame = frame or CreateFrame("Frame")
frame:SetScript("OnEvent",function(self)
if not LFGListFrame.ApplicationViewer.AutoAcceptButton:GetChecked() then
LFGListFrame.ApplicationViewer.AutoAcceptButton:Click()
end
self:UnregisterEvent("LFG_LIST_ACTIVE_ENTRY_UPDATE")
end)
frame:RegisterEvent("LFG_LIST_ACTIVE_ENTRY_UPDATE")
end)
end)
end

Here are two other useful macros (not related to this addon)
/script ResetInstances();
and
/script SetLegacyRaidDifficultyID(#)
Replace "#" with the number: 
3 - 10 Normal
4 - 25 Normal
5 - 10 Heroic
6 - 25 Heroic 

For those new to mount farming on alts, here's a link to Asmongold's guide
Thanks to Ro/Gello of Underhill for the original code.

Also check out Leaderchange