How to change frame mounted gear shifters to brake lever shifters

[screenman]

I have Sora on my 6 speed turbo bike, they just have an extra click the does nothing as the stops will not allow the mech to go further down.

 

[rh100]

I've done smilar operations on several bikes.
Cold-setting a steel frame is not difficult, even mixing Campag & Shimano is not that hard if you read up on it carefully.
BUT
If your existing downtube shifters are the band-on type (rather than the type which screw directly into a boss on the frame) or if your rear derailleur mounts directly to the rear wheel axle (rather than to an threaded hanger that projects below the drop-out) then the whole thing becomes very much more problematic, and IMO the horizontal drop-outs make the frame much better suited to conversion to a fixed wheel/SS operation.
If that's the case and you don't want a fixed or single-speed and the frame is of good quality (Reynolds or Columbus tubing for example), then you should be able to sell it on the eBay (as suitable for fixed conversion) for a decent price to partially fund something that better suits your needs.

A search of eBay should bring up some band on cable stops, a hinged clamp that is more functional than pretty but doesn't look too bad, for a few quid it solves a problem.

It's a worthwhile project, when looking into converting one of mine, I was going to go for some bar ends either ultegra ( I think) which were friction or index but look a bit ugly, or some dia compe or rivendell which are much nicer looking IMO, but friction only. Both would have been about fifty quid and I managed to get some barely used 2300 sti's instead for for the same price so went for those. Those will also have a spare click as are 8 speed on a seven speed cassette.