That kind of trick is perfectly acceptable IMHO but watch the tolerances. lack of hysteresis/feedback makes this slightly less predictable and you may have to play with the values and measure the timings under load conditions to get optimum values.EDIT: The threshold for the NCP1521B enable pin is .7v. Could I just use a charging capacitor on that w/ a current limiting resistor?
Once optimised it should be consistent with those components, but beware subtle changes in components choices can often catch you out later..
regards
Al