It's your network, do whatever compromise is required by you, your management, and their budget.
I agree with comment above: don't mess with hidden wire, do it close to the phone or in the patch panel. [EDITED re safety] Be aware any legal consequence of non-professionally made cabling, especially as regards fire hazards. But because the power is allowed to be whichever way round (by 802.3ag), that itself isn't an issue: it's only the pre-standard phones which require it to be a particular way. From memory it was a fight between Cisco and another company about which way the polarity was, and the result was a late amendment to permit either polarity.
So 802.3af specifically says that "Alternative B" power (ie, 4+5/7+8) can go either polarity, and that it is up to the Power Sourcing Equipment (PSE) to decide whether to do A or B and which polarity.
So you had better check (empircally) what power your POE-supplying switch actually delivers, and whether it powers the phone -- 802.3af has pretty complex startup behaviour.
If that doesn't work, you could consider "Nasty Cisco Power Patch Panel", which you'll find available as mid-span injectors, or easy to do with a punch down patch panel and a suitable power supply.
My notebook tells me this about 802.3af
Details from standard, originally 802.3af 2003, now folded into 802.3 2012
- Alternative A: power is on 1+2 and 3+6 data pairs
- Alternative B: power is on 4+5 and 7+8 'spare' pairs
- section 33.2.3: "A PSE shall implement Alternative A, Alternative B, or both"
- section 33.3.1: "The PD shall be capable of accepting power on either of two sets of PI conductors."
- "The PD shall be implemented to be insensitive to the polarity of the power supply and shall be able to operate per the PD Mode A column and the PD Mode B column in Table 33–13. [polarity either way around]"
- "PDs that implement only Mode A or Mode B are specifically not allowed by this standard."
- "PDs that simultaneously require power from both Mode A and Mode B are specifically not allowed by this standard."
Let us know how you get on.