Pass username in the request body payload for creating receipt write off

We have a requirement to create receipt write off as per the user we get in the inbound file of OIC. However, we cannot have multiple connections for different users in OIC. So, is there a way the user can be passed in the request body payload of the standard receipt api (we also will not be having access to the passwords for those users) so that the receipt write off is created as per the limits of that user but for authentication we continue using the common user.