I pulled a sneaky on my friend's Diamondback road bike. I had a set of 8sp Sora brifters kicking about that were some hundreds of dollars cheaper than buying new and somewhat more user-friendly than his old downtube shifters.
Unscrew or drill the rivets out of an 8sp cassette body, add a thin spacer first 1 or 2mm perhaps, then 7 cogs of your choice with the correct spacers salvaged from the cassette and then your lockring. Set the high and low limit screws accordingly and nobody would know any different. Scrub the "8sp" label off the right-hand shifter if it bothers you.

Remember to also fit an 8sp chain!

The benefits of this are great.
1. You get to use readily available brifters on an old system
2. Future proofed for a new wheelset. Upgrading will let him have his 8 speeds as desired.
3. Cost-effective!