1099-B with 100s of transactions

You have multiple options. If the 1099-B has summary totals for each category (A - short-term covered, D - long-term covered, etc.) then you can just put in those totals. 

There is also with Form 8453 a way to enter in summary totals and then within 3 days, mail with the 8453 the supporting documentation.

And yes, some people do the attachment as you said, but it's the input totals by category that are the most important.

Look at page 11 of  IRS Schedule D instructions for line 1a and 8a  

I'm surprised that this question still pops up so often after all of these years.

totals for short term covered, short term noncovered, long term covered and long term noncovered

if the pdf would be a very large file you can check the box on schedule d to kick off form 8453 and mail a hard copy of the brokerage report 

To be a bit more specific, only the NON-covered transactions have to scanned/attached - or mailed.

And be on the lookout for any wash sales on those & adjust accordingly.