Can you create wood conditioner from DIY wood sealant?
I've experimented with oiling wood (for a few years, about ten years ago) and I've never seen oil make the wood rancid (I know wikipedia says it does), but if it's a concern use mineral oil (which won't become rancid). The real drawback is that any-old-oil only yields a temporarily wet look (for a few months). Using an oil based varnish will allow the wood to appear like it has been freshly oiled in a permanent way. I've experimented with several drying oils and shellacs. Incidentally, (true) shellac is a natural substance obtained from the lac bug. For furniture, shellac is kind of a nice sealant.

You can thin oil with paint thinner, but that totally defeats the no VOCs. Also, the wood will absorb the oil after a while and the wood will look dry again even if you cover it with (a water based) varnish. Using blown or boiled linseed or tung oil will make the oil form something closer to an epoxy like resin (in a crude/primitive kind of way). 

Siccatives are used for drying oils (chemistry becoming more modern). When I was a kid I used to see japan drier everywhere... I think it's a relic now (look in an art store or get it online). Anyway, something like that is what I would use with (raw) canola (to help it "dry" and make the finish last longer). The funny thing about driers is that they keep it looking wet longer.

The final word: experiment with wood blanks.