step up rings?
I've had no problem using step up rings with my NEX-6.
I've got a 46mm polariser and 46mm variable ND filter that fit my Sigma 30mm and 19mm. But I use a 40.5mm to 46mm step up ring to use those same filters on my 16-50mm PZ OSS.
I have plenty of larger filters and a Cokin P filter holder system too and I've used those on all the lenses I just mentioned using a variety of step up rings.
Plenty of inexpensive rings on Amazon or eBay.