unfortunately, it's currently not possible to use UTC (absolute) offsets.
Those relative offsets are all it can do for now. (and they only adjust the hour, not the displayed day / any date format)
Here's a feature request regarding UTC: #154
I might consider to implement it soon though... after the next final release and without the format rewrite I had planned... but I guess one more format shouldn't hurt that much (and it's taking me way to long to do anything anyway)