grazanaut:
For example, the ALD1108E, or any of the devices listed at ALD EPAD High Precision MOSFET Arrays
I did read the app note only briefly but as I understand it the device is only one time programmable - you can increase the stored charge but not remove it.
To get a floating gate transistor you simply take a transistor and let the gate float - what more it should do? If you think it does not hold the charge long enough you may boost the gate source capacitance with a cap and minimize leakage paths - by careful choice of the transistor and removing any outside impurities and proper sealing of the gate. I believe very very low leakage currents are possible if done right.
And MarkT is right - when you see a silly question you first try to get clarification. If someone asks for a sword sharp enough to cut nails you should ask if they know dedicated scissors exist. Beginners are too often (pleasantly) surprised. Or they are trying to do something impossible or very difficult.