Need to lay a portion of my high-end speakers cable under the floor ...

My [unfortunate] listening room layout means I am >compelled< to lay the middle third of my high-end speaker cables [2.5m each] under the floor. Sadly, this (non-ideal) arrangement is unavoidable (not least for safety reasons). I plan to have a 1 to 2 inch diameter duct (plastic or wood) laid down under the floor to act as the cable conduit over this mid section.
Apart from the fact that this arrangement genuinely sucks, are there any tips, experiences, tricks I can do to ensure I minimize the inevitable downside from this unfortunate situation? (Yes, moving house is an option ... moving listening room is not).
Is there any "conditioning" I can do to the underfloor conduit before hand to minimize detrimental distortion? Will raising the exposed cable segments be a total waste of time? System has Nordost SPM2s, but I will be upgrading soon (Ansuz perhaps) feeding Raidho D3s. Any ideas welcome.