"How do I make TT report a corpus distribution from a complex trust without an income distribution?"
It is not technically correct, absent the circumstances set forth in the instructions for Form 1041 (link below), but with TurboTax Business you can make several overrides in Forms Mode on Schedule B. Obviously, you want Line 15 of Schedule B to be blank (or otherwise show a zero).
https://www.irs.gov/instructions/i1041/ch02.html#d0e4239
You should be aware, however, that distributions, whether mandatory or discretionary, carry taxable income through to the beneficiary(ies) to the extent of DNI.