G’day,
It is worth pointing out that 60m slabs can be toproped with a 60m rope, not 30m slabs. Of course the belayer needs to sit on top.
Since the difference between leading and toproping is basically COMMITMENT, hence leading with preplaced static is style-wise same as toproping (get scared=grab static line=no commitment) and would be considered a FTRA (first toproped ascent) not FA (first ascent). Practical implication is that someone can bolt it and climb it with bolts in the future and rename it and get their name on the climb and you are forgotten history-wise.
Of course that does not mean that you cannot do this and have fun, as history-wise we will all be forgotten in a hundred years or so anyway.