For my analog Diceware I typically incorporate some random capitalization. I do this via dice rolls as described on the original Diceware FAQ. I think this would be a useful feature for this generator. I envision an added button which, when clicked, would randomly capitalize a letter in the current passphrase. Clicking it again would capitalize a second letter, three times a third letter, etc.

Another option might be a button to all-caps a random word, if a single-letter option is too much effort.