Dear Swathi,
1) If you are hard cording the currency in the query it wont work ( it wont even give you the output)
2) First of all check whether what is the unit maintained for your keyfigure A_STDCOST.
if it is 0currency for the keyfigure A_STDCOST then you can hard code it in the remote cube in either transfer rules or in the update rules as USD.
If you A_STDCOST doesn't carry 0currency and carries some other unit then bring in constant USD is not going to help you
3) the other simple option is to maintain the description as SEP FC in USD in BEX. You can make the A_STDCOST keyfigure as a formula using NODIM .
Regards
Gajesh