If you're suing it as a spare, then it's just to get you home or to the garage, so it would be ok.
1/4 of your Jeep will go backwards.
Problem is that you have different tyres that have different rolling radius, which would not begreat for an LSD or locker (if it's got one). On the front it may affect the steering negatively.
always have spare direction set for nearside as statistically tyres nearer the curb are more likely to puncture, but don't panic as it will get you home on either side, you will only notice a difference at high speed or in adverse conditions
buy a can of tyre weld or join the AA, lot less hassle than carrying 2 spares
If it bothers you just buy a none directional tread spare
In the Swedish Army it's considered normal to put the front directional tyres the wrong way.