Hmmm.... Older books gathering dust: Japanese for young people - no mention of わたくし at all, Japanese for dummies does refer to it (and it does say formal), but no mention of actual processes. The examples in the "Basic Japanese → English dictionary" (Oxford/Japan Foundation) DO have は after わたくし, so does Websters... Oh well, a floor covered in books, few of which even mention わたくし - I'll put it down to "I misread something" unless it shows again somewhere.
A Dictionary of Japanese Particles, Sue A. Kawashima, Kodansha
3 distinct uses,
emphasises an explanation, or a cause of events/actions
expresses desire or will
and (no surprise) at the end of a sentence, as an exclamatory particle.
「でゆうんだ」は 「ってゆうな」べき です かもしれない。 調査している