I just discovered that Eizo has added a procedure for profiling tablet displays, phones, etc. to their new ColorNavigator software. They call it Media Emulation. ColorNavigator is the free profiling software that works with their higher-end monitors like the "CG" series. With this feature, you can choose an option for "Create ICC profile for tablet/display device..." and the software will send a series of color patches to a web site that your tablet can access. As you place your measurement instrument on the portable display, ColorNavigator will read the colors and create an ICC profile.
Now you have a means of profiling these displays even though you cannot connect a USB measurement device directly to them! You can use the resulting profile to "soft-proof" what your images will look like when they are viewed on these displays. Available on the latest version of ColorNavigator (version 6.1.1).