the short answer is that if you need (want?) to file the 751 statement you must mail it in with your return. it can not be filed separately and as you have noted it is not an option on the 8453. the statement is not an IRS form or schedule so even if Turbotax wanted to include it in its apps there may no way to transmit it electronically.
since millions of shares of PTPs/MLPs are sold every year and every sale requires the 751 statement, the IRS could ease the taxpayers' burden by allowing either a check "the 751 box" on schedule E for the partnership i or create a "751" schedule or form that could be e-filed. I'm guessing but since yours is the first I've seen about the 751 statement issue, many others probably don't know they're supposed to file it or don't bother to.
