It depends on if you want to do it the way that is technically correct, or the possibly 'close enough' way.

Technically correct: 

File Form 3115 to change the prior years to 39 years (although I would need to research if that is allowed because it is changing this year).  Then for the change this year, you have the option to (a) continue with 39 years or (b) restart everything using 27.5 years and the ADJUSTED Basis (reduced for the prior depreciation, although you don't actually enter the prior depreciation into the software).  If you restart things for 27.5 years, that applies to the entire year.

The possibly 'close enough' way:

1) One option is it just put the entire year's depreciation on the second property.

2) The other option is to split it as you said, but for THIS year, don't enter any prior depreciation.  Then NEXT year, change it to the original/old placed in service date and enter the total prior depreciation.