Yes it is possible; you can even buy adapters to do this for you. But -
1) You mustn't split the pairs (i.e. each matching pair pf pins in the standard must use a twisted pair of wres within the cable, not one wire from one twist and one from another)
2) There are some schemes, such as the older methods of providing Gigabit ethernet, that do use all eight pairs. You must make sure you're never going to need to use such things in your installation before you do this
3) It's only really going to work up to 100mb/s; I wouldn't want to try this at Gigabit because the crosstalk would likely be too high for reliable operation. Depends on the cable length and what you're doing.
So yes, you can, but it's a bodge. And if you go by the letter of the standards (which for a commercial, professional installation you should be) then no you can't