asp.net webrequest form post

how would I construct the following ebay upload using a webrequest?

POST /path/to/upload/script HTTP/1.0
Connection: Keep-Alive
User-Agent: My Client App v1.0
Host:
https://bulksell.ebay.com/ws/eBayISA...ExchangeUpload
Content-type: multipart/form-data;
boundary=THIS_STRING_SEPARATES
Content-Length: 256
--THIS_STRING_SEPARATES
Content-Disposition: form-data; name="token"
12345678987654321
--THIS_STRING_SEPARATES
Content-Disposition: form-data; name="file";
filename="listings.csv"
Content-Type: text/csv
... contents of listings.csv ...
--THIS_STRING_SEPARATES