Very low power voltage regulator - diode?
Consider using a basic linear low quiescent current regulator. You probably know that linear current regulators basically "burn" the excess voltage which can be a problem when stepping down from a higher voltage like 7V, but remember that the power dissipated depends on the current (P=IV) which in your case is extremely low. At 5uA, you'll be burning (7V-3.3V)*5uA or 18.5 micro watts.

I've seen voltage regulators with extremely small quiescent currents, in the &lt; 10uA range, and even those could supply 100mA continuously.