I've talked at length with a few battery manufaturers about this very topic (Exide, Interstate, Orbital,) and they all agree that winches should go right to the top posts.
You've noted the problem with that thinking, WRT OEM cables.
This is why all WiP cables (one of the reasons, anyhow) are terminated with ring lugs - and then you are able to use marine-style, military-style, or universal (flat)-style clamps to attach cables to the battery itself. That's the best thing I can suggest - reterminate the OEM leads with ring lugs (they should be 8AWG - the very upper limit of what can easily be done with hand tools anyhow) and convert to a binding post-style battery clamps.
Attaching winch leads to side posts was very much not recommended - the side posts (in batteries so equipped) are generally good for 75-80A constant draw, 150-160A very intermittently, and winch loads can melt the pads right out of the case (at 300-700A for a full pull, depending on winch model and load.) This is from conversations that included Ramsey and Warn - and they had side posts melt right out of the case in testing (with the battery in free air. Underhood will generally increase ambient temperatures by 30-40*F, and that's going with a mild to moderate reduction.)
Retermination and conversion of attachment is the best advice I can offer you offhand. Replacing battery cables outright (going to a larger size) isn't a bad idea - but may not be strictly necessary, unless you've uprated other components of your electrical system as well. If you want to go with that option, click the link in my sig to find out more (if I don't have a listing for your vehicle, that's because no-one has ordered cables for it yet and confirmed fitment. It can certainly be done - I just need the measurements to make it all work, and they're easy enough to get.)
"recon" (sic - reckon)(tm) "hihgly"(tm) "seceed"(tm)
"Outback AIDS - Alcohol-Induced Dizzy Spells"