I can do that for most of the girls, especially the averted!Harem, since they distrust him they don't even use honoriffic. (Cecilia is an exception, but you know her...
)
And of course, mandatory mindscrew humor where they DO refer to each other as Ichika when talk to each other
Fem!Ichika: "Ichika, wait a minute'
Ichika: "What is it Ichika?"
Girls: "????????"
Thanks.