I'm not understanding, your currently on a CPT (student visa work experience) visa and the same employer will hire you on H1B in October?
You want to change to a new employer now or in October? Right now my guess is that you cant, CPT visa's are employer specific (so is H1B). If you want to change employers, waiti till the H1B is in effect and petition the new employer to have the visa transferred to them.
The H-1B Portability Rule: How to Change Employers
Right now you are still on CPT, so talk to the school if you want the work experience shifted to a new employer.