You don't get it, do you?

You don't build the rocket at sea level and truck it up there. You build a rocket assembly plant at altitude. Remember that (one of) the chief weakness(es) of the space shuttles was the remote fabrication of the boosters and their shipping in subunits before final assembly on site.

I realise there are major issues with oxygen availabiliy near the summit, but these issues are tractable given either a selection of Peruvian and Tibetan employees or supply of oxygen on-site or a lower-latitude assembly site with a dedicated constant grade incline to raise the assembled rocket up - like the Apollo crawler, but uphill.

Of course, there would then be a large town perched high on the flanks of the peaks of Hawai'i.

The point is, this is no more absurd than your pipelauncher.

Any added component to a launch system MUST offer sufficent advanges to offset the disadvantages of another "stage" which has to be timed in synchronicity with others and has its own failure paths.

I am far from convinced that the sub-1% advantages of a spring loaded launch system (which is what your pipelauncher is) is worth the added complexity and failure routes.

Note also that the entire launch system will have to be marinised. For Zenit and Sea Lunch - they are reusing an existing (small) lunch system which has ALREADY been marinised for its original esign as a sea-launched ICBM.

Now try doing that with an Ares-scale launch system...