Specifically any good tips on removing a couple of water bottle holder bolts that just turn in the thread of an aluminium frame without unthreading.

Impossible to get any purchase with pliers, should I drill into the bolts or is there something simpler? Thanks.

It sounds more like the threaded insert is spinning within the frame?

http://www.parktool.com/blog/repair-help/water-bottle-fittings

depends on how steady you are with an angle grinder… cut a small notch and flat blade screwdriver it out. Might mean sacrificing the holder though.

Thanks for the advice, will give it a go.

Grind a slot then use a flat blade screwdriver or flat blade bit with a breaker bar or ‘T’ bar. DONE!