Sounds like your idea to use rubber hose is a reasonable solution providing its size matches the existing repose height of the typebars. The KMG is a tank and a very nice typer; one of the most filthy, well-used machines I ever bought was a KMG and it cleaned up really well. Mine had a full blown mouse nest in it, every part crammed full of the detritus of rodent housing, but a thorough cleaning and maintenance revealed a typewriter that could easily be my daily typer if it wasn't for the SG1... 

UPDATE to the subject of this thread.
I removed the typebar rest, thinking it would flake away but it was really just covered with what appeared to be a coating of white out and eraser shavings. I used some rubber rejuvenator on it and it cleaned right up. It is actually pretty supple rubber, considering its potential age. No fabrication of the rest is needed, thankfully.

As for the typewriter itself, I spent a few hours early this morning scrubbing the machine gently with a sponge and soapy water, while listening to the radio and drinking a couple cups of coffee. It's not pretty but it's clean. I got the segment cleaned out, slot-by-slot, with an xacto knife and a lot of patience. I think I pulled out about a tablespoon of formerly-packed eraser material mixed with ancient ink and white out. Amazing how much volume is shared by those slots. I used a rocket blower (for photography use) to gently ensure the individual slots were clear, then I hit it with some graphite. I scrubbed the slugs with a toothbrush and some windex since I can't use the maxpro stuff indoors and didn't feel like taking the machine out to the backyard. I used some synthetic watch oil (which I use on camera escapements) on as many moving points as I could find. The main carriage track got a very fine smear of moly grease for the support bearings.
I rolled a ribbon onto the old spool and stuck a sheet of paper in.
I knew this was an elite typeface since I had seen the 12 on the escapement wheel while cleaning the carriage but was still surprised when I saw that everything was working almost perfect. The left carriage height adjuster (term?) needs to be turned in about 1/4 turn then the lower case letters will be aligned perfectly with the upper case. Ribbon vibrator works well and doesn't stick or drag. Everything is great.
Being my first standard size typewriter, I was so pleasantly surprised at how light the touch is. These keys just need to be tapped and they will fly to the paper. 
I'm very happy with this great typer.

Phil Forrest