NOT SURE if I UNDERSTOOD YOU CORRECTLY ....
BUT Making sense out of your concerns -- this is what I can to tell you .....
CONSULAR PROCESSING (in simple terms) is just a way to get visa to enter US while the applicant is outside of the US or has plan to travel outside during any immigration related applications. When you file your h-1b, you select the option to consular processing or change of status ( since your are already here) and when it is approved then you are in h1-b status starting October 1st of that fiscal year. From my understanding you cannot change that date, meaning that you cannot request a start date, unlike OPT. The only exception is that for any reason your h-1b petition was audited and then they send you the approval after the October 1st. In this case your start date would be the date that USCIS choose, which is usually few days after the approval notice was send. I have seen people with start date as late of April and May of next year.
So back to your question - No, you cannot use your OPT until next June 2015. Now you are no longer an F1 after October 1st. You will be in h-1b.
So again, there is no harm in doing consular processing since it's just like a visa interview; you get the visa, (and actual change of status actually happens I guess in a port of entry; I'm not sure on this.)
Alternate route if you want to use your OPT until next year : Apply next year h-1b quota. Since your opt doesn't expire until June 2015, and provided that you file h-1b in 1st week of April, and has received notice, you can continue to work until 1st of October because of "CAP-GAP" rule. Make sure to select consular processing during filing, go to Nepal and do visa interview.
The only drawback is that if for reason the h-1b went lottery system and didn't get selected then you are out of luck when your OPT expires in June 2015.
Not sure why you want to work on OPT and delay your h-1b? If you are concerned about your OPT expiring before next year October 2015 ( when actually the h-1b starts) then you are covered by CAP-GAP rule. But if you still want to do this year that I would suggest you to do the change of status and then go back to Nepal for visa stamping. Its much easier..
Hope this helps..
