I spoke to my friend about this issue earlier this week. He is done at Team Highroad (other than sending me my stuff next week
) and is just getting ready to spend 2 months in Oz setting-up Greenedge.
At Highroad, they just used the stock version of the cable routing seal. He said that it was 'fully-sealed' and that they never had an issue with either fouling or water ingress into the frame, even in the Northern Classics. I asked whether the Team bikes (which are all McLaren-versions, even the ones without the obvious 'McLaren' colour and logos) were different than the other Venge frames. They are not.
All of the Venge bikes (McLaren, S-Works and Pro) are produced using the same moulds. I was a bit suprised by that, as I thought McLaren would have tweaked the aerodynamics of its frame. Not so. Apparently, McLaren's input into the design of the Venge was only in the choice of the carbon fibre and the layup schedule. Interestingly, this was said to have been a real eye-opener to Specialized, especially as its 'gurus' also come from other leaders in the composite industry. The composite technology and know-how in F1 is superior to that in aerospace or the military, which was also a suprise to me. In an industry that has come to expect the 'aggregation of marginal gains' from subsequent iterations of framesets, the input of McLaren is said to have been revolutionary, not evolutionary.
Anyway, the point is that the sealing of the cable guide system on the Venge is fine even for riding in the worst spring weather in the World Tour, so you should be fine.