I’ve been trying to implement Marc’s answer without any success, but I found some help from a similar question: capybara: fill in form field value with terminating enter key. And apparently there was a pull request from capybara that seems to address this issue.
What worked for me was:
before { fill_in "some_field_id", with: "\t" }
My example erases the text in the field and then presses Tab. To fill in a field with 'foobar', replace "\t" with "foobar\t". You can also use "\n" for the Enter key.
For your example, you could use:
find("#element_id").set("\t")