I found a way, but it is very janky and volatile. After it is bound it can reset if you try to make changes to it. if you try to click on the macro in icue, it will unbind it.
TLDNR - Make a macro, bind it to a mouse button. Go to users/appdata/roaming/corsair/CUE/profiles , Find your cueprofile. change the button you bound, to Mouse1.
For safety: Rebind one of your dpi keys or sniper button or forward/back buttons to act as your left mouse button. I also make one of my keyboard media keys backups for all the mouse buttons. Or make a profile switching action that goes to another profile.
Then.
Make the Macro you want to take the place of the left mouse button.
Bind it to your middle mouse button.
Export your profile somewhere and open it up.
Find the ID of your profile.
Close icue.
Now find the .cueprofile in users/yourusername/appdata/roaming/corsair/CUE/profiles
open it up, ctrl+f search for the name of the macro you made. It should be in one <first> branches of the <value#> branches under <Actions>. Inside the <second> branch, you should see:
<first>Mouse3</first>
<second>Click</second>
change the Mouse3 to Mouse1. Save it
-<cereal>
-----<value0>
---------<profile>
---------<name>Your ProfileName</name>
---------<id>{63f8eRandom01-stuff1-b774-56dfds501638}</id>
--------------<properties size="dynamic">
++++++++++++++<value0>
-------------------<value1>
. . . . . . . . . . . . . . . . <key>Mouse</key>
----------------------------<value>
--------------------------------<properties size="dynamic">
+++++++++++++++++++++++++++++++<value0>
+++++++++++++++++++++++++++++++<value1>
+++++++++++++++++++++++++++++++<value2>
+++++++++++++++++++++++++++++++<value3>
++++++++++++++++++++++++++++++++++++<polymorphic_id>random#'s</polymorphic_id>
----------------------------------------------<polymorphic_name>ActionsProperty</polymorphic_name>
----------------------------------------------<ptr_wrapper>
--------------------------------------------------<data>
--------------------------------------------------<Actions>
-------------------------------------------------------<Value0>
-------------------------------------------------------<Value1>
-------------------------------------------------------<Value2>
-------------------------------------------------------<Value3>
------------------------------------------------------------<first> your macro name should be 3 or 4 layers deep into the <first> fold/branch.
------------------------------------------------------------<second>
------------------------------------------------------------------<first>Mouse3</first> change this to Mouse1
------------------------------------------------------------------<second>Click</second>
------------------------------------------------------------</second>
-------------------------------------------------------</Value3>