Font::layout coerces lifetime for "str" parameter

The Font::layout method currently forces the str parameter's lifetime to be at least the font's lifetime, which makes it impossible to use it with a string created on the fly:

let vec_str: String = vec.iter().cloned().collect();
let glyphs: Vec<_> = font.layout(buffer_str.as_ref(), scale, offset).collect();

where vec is a Vec<char>, triggers a lifetime error:

error[E0597]: `vec_str` does not live long enough
  --> src/render/mod.rs:33:35
   |
23 | pub fn get_glyphs<'font>(vec: Vec<char>, font: &'font rusttype::Font<'font>) -> Vec<PositionedGlyph<'font>> {
   |             ----- lifetime `'font` defined here
...
33 |     let glyphs: Vec<_> = font.layout(vec_str.as_ref(), scale, offset).collect();
   |                          ------------^^^^^^^-------------------------
   |                          |           |
   |                          |           borrowed value does not live long enough
   |                          argument requires that `vec_str` is borrowed for `'font`
...
38 | }
   | - `vec_str` dropped here while still borrowed

Would there be a way to fix this, while keeping the guarantees brought by !140 (merged)?