Default [Q] Is there a custom ROM where read-only storage can be created

Hi, I have a quite specific request. You certainly know that Google now restricts access to external storages - they are read-only. It is quite common issue on devices with Kitkat and two more external storages. Custom roms developers workarounded this and sd cards are read-write. But I am an app developer and I don't have any device where I can test the Google's restriction. Is there any 4.4 ROM where I can make the external storage read-only? I.e. on external storage, that the only writable directory for my application will be it's application dir in /Android/data/com.foo...

I tried Cyanogenmod 11 and tried to edit /system/etc/permissions/platform.xml because everybody advice to add group gid="media_rw" to WRITE_EXTERNAL_STORAGE to make SD card writable. So I thought that reverse action (i.e. removing the groups) will make it read-only. But there is nothing to remove .. it doesn't contain this group.

So I tried to change the permissions directly but SD cards use FAT and permissions cannot be changed.

Could you please help me? I would appreciate any advice. I really would like to have a device where I can test this stupid Google's restriction. Thank you !