Most simple way would be to use a macro instead of rotation. You can switch to macro in the gathering preset and then type in the keypresses you want to execute. This however is not very failsafe when you move your mouse a lot.
For the second method you would need to share your rotation as edgedy mentioned.
You could fake a rotation using 850GP instead of 900GP for example if the last skill you are using costs you 100GP:
Create an Ingame-Macro like this:
/micon "Field Mastery"
/ac "Skillname you want to use instead"
and either replace your Field Mastery Skill with this or put it before it on the hotbar. Then use Field Mastery as the last Skill in the rotation builder. This will trick Miqo into thinking you want to execute Field Mastery using only 50GP, but instead you will use the Ingame-Macro and execute your skill.