楼主你这个不能叫split rollover，这应该是一个early withdrawal + partial rollover。
withdrawal部分对应1099R Box 7 code B, partial rollover对应1099R Box 7 code H。
rollover部分只包括earning，这个irs是支持的。irs 对partial rollover默认是untaxed portion优先，在roth 401k->roth ira也就是默认earning会被先rollover。
A partial rollover of a nonqualified distribution is treated as consisting first of the untaxed portion of the distribution.
Example: Joe receives a $14,000 eligible rollover distribution that is not a qualified distribution from his designated Roth account. The distribution consists of $11,000 of Joe’s own contributions to the account (his investment, which has already been taxed) and $3,000 of earnings on the account (which has not been taxed). Within 60 days of receipt, Joe rolls over $7,000 of the distribution into a Roth IRA. The $7,000 is deemed to consist of $3,000 of earnings and $4,000 of his contributions. Because only the portion of the distribution that would be includible in income is rolled over, none of the distribution is taxable to Joe.
所以earning做了这个partial rollover，它不能算在401k的basis，进了roth ira会变成里面的earning，59.5岁也不能无税无罚取出来。
本金的话我觉得主要问题在于hardship withdrawal能不能算eligible rollover distribution。
实际操作的话可以用hardship withdrawal先取钱，60天内把收到的earning部分+withheld tax存到roth ira里面。但不知道这样做有没有违反什么规定。