Congrats! Yes it can be done without the Epi. In fact it often goes faster is you don't get one. I went from 2cm to 10 in 45min on my second child with no meds. The first started fast until they gave me the Epi then it stalled to 1cm an hour.
So, the rule of thumb of 1/cm per hour is WITH the EPi.... hmmmmmmmmmmm....and thanks!!