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I'm trying to lay out a block of several lines of all-caps copy. I want the lines to be evenly spaced. However when letters such as Ô and È are included in a line, they "collide" with the preceding row.

Here's a quick example:

Are there any rules of thumb for handling this?

In some cases, for example, in publications headlines with a colored background close to the text limits, the height of the accented letter is reduced. As far as I know, it's the only one rule.

In highlighted texts such as the one in question, if the space between text lines has the same distance/height, what in different text sizes it is not the same leading; the equality between the separations creates a repetition pattern optically stronger than the proximity between accents and letters.

Try fixing your text with this optical adjustment, taking as a reference the largest line spacing.

If you don't have a lot of text to deal with or if you can modify the font, you could also tweak the accents so they take up less vertical space. Just make sure that they can still be recognized for what they are.

Here are some examples in use 1, 2, 3

They'll still take up space in your leading but you'll get a consistent cap height and won't have them collide with the previous line.

Really your only option here would seem to be to increase the leading. You can get titling fonts that have custom condensed accents. Fonts In Use shows some examples: e.g. see this modified umlaut in a German case, but I don't feel that fits with the design of your font. It's quite airy and spacious; my feeling is that this kind of modified accent tends to go best with bold geometric fonts, where people are willing to take a bit more abstraction from normal alphabetic forms.