Part of my brother's response which is relevant in particular to including the sources for the "per saltum" etc.:
"Leo XII treats of this as something of an unsettled question in his response to Anglican ordinations, Apostolicae Curae, but even so it seems reasonable to err on the side of caution.
"It is not relevant to examine here whether the episcopate be a completion of the priesthood, or an order distinct from it; or whether, when bestowed, as they say per saltum, on one who is not a priest, it has or has not its effect. But the episcopate undoubtedly, by the institution of Christ, most truly belongs to the Sacrament of Order and constitutes the sacerdotium in the highest degree, namely, that which by the teaching of the Holy Fathers and our liturgical customs is called the Summum sacerdotium sacri ministerii summa.(Apostilicae Curae S.28)"
The position from the supplementum to the Summa Theologiae is a little stronger in favor of the fact that the case of the elevation of bishops is different from every other order: "One order does not depend on a preceding order as regards the validity of the sacrament. But the episcopal power depends on the priestly power, since no one can receive the episcopal power unless he have previously the priestly power. Therefore, the episcopate is not an order." (ST III Sup. Q.40 A.5 Sed Contra)"