I don't think you can put in 6700 since the max is 6500 but perhaps you can do the 6500. from
https://www.irs.gov/retirement-plans...ibution-limits
there is only this restriction:
For 2015, 2016, and 2017, your total contributions to all of your traditional and Roth IRAs cannot be more than:
$5,500 ($6,500 if you’re age 50 or older), or
your taxable compensation for the year, if your compensation was less than this dollar limit.
Later in the article some other limits on Roth contributions are linked but the link only refers to your MAGI, not the nature of your Roth401K.
I'd vote w/ LOL that you can do it but if you want a real answer, post your question at the retirement forum at fairmark.com and look for Alan S. answer.