Unable to hide non-catalog req line in sourcing

Hello,

Due to existing customer processes which we unable to change we have such case as:

When creating RFQ (Auction) from non-catalog req buyer adds new lines manually (via xls upload) which  he would like to receive bids for. The initial non-catalog req usually consist of only one line which represents 300+ real lines and serves mostly for budget control check so, unfortunately, we can't replace this initial req line from catalog in sourcing as it would cause to add 299 line manually. We also  unable to cancel this line because we''ll lose documents link. The problem is that this particular line should't be shown (and answered!) to suppliers when negotiations are not restricted by invited suppliers (then