How do I write a cover letter and interview for a position that I obviously intend to leave when I find something better?

So I have a degree in electrical engineering. I am having trouble finding an EE job in my preferred area and would like to find something to tide me over until I can find one (food service or retail. Something small like that.)
I’ve been trying to find an EE job for months (promising interviews for it have been just frequent enough that I haven’t already found a job like this.)
I’ve been interviewing for jobs that I intend to stay at, so I’m out of practice when it comes to applying for part time temporary jobs. I feel like it’d be disingenuous to write my cover letter and answer interview questions like I do for my past interviews. (“Where do I see myself in 5 years? Working my way up that ladder and learning new skills of the trade. At this Chili’s. With my engineering degree.”)
How do I write cover letters and do interviews and impress potential employers without sounding totally fake?

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