changing the value given by date("U") without changing the server time

ive been using date("U") allover my script when suddenly i found that i need to add timezone option in the website , which means all date("U") should look like date("U") + $someTime , is there any way i could change the time that the option date("U") displays without the need to modify the date("U")'s in the script and without modifying the server time ?

something like setting the date read by the 'date' function + or - some h开发者_开发百科ours ???

date("U") gives you the seconds since the Unix Epoch which is in GMT. How is the timezone relevant here?