BSS would be an export of services as long as the recepient is outside India, monies receivd in CFE + services used outside India ( benefit accrues outside).
Once it is export, the refund/ rebate is possible. Refund under Rule 5 of cenvta credit rules Reabte under notification 11 & 12 of 2005 in service tax.
Form R ( central excise) maybe used setting out the cliam and all the grounds on which claim is tobe made. To be accompanied by proof of export, FIRC, ST-3 filed disclosing required actions. A statement of credits though not reqd under law may also be provided to avoid further delays
Presnelty there is invariably a delay in processing the claims. Unless they are quite high ( over 5 lakhs) not recommneded at this time. Of course if claim made late only option of rebate on service tax paid ( utilisaing the credit) exports can be claimed. Other options closed.