How can I get Dapper to map .net datetime to datetime2?

Dapper is litterally a single file that you include into your code base. Just edit the file:

Replace (around line 300):

        typeMap[typeof(Guid)] = DbType.Guid;
        typeMap[typeof(DateTime)] = DbType.DateTime;
        typeMap[typeof(DateTimeOffset)] = DbType.DateTimeOffset;
        typeMap[typeof(byte[])] = DbType.Binary;

With:

        typeMap[typeof(Guid)] = DbType.Guid;
        typeMap[typeof(DateTime)] = DbType.DateTime2;
        typeMap[typeof(DateTimeOffset)] = DbType.DateTimeOffset;
        typeMap[typeof(byte[])] = DbType.Binary;

Edit:
There's also a nullable DateTime further down that block of mappings, around line 319:

        typeMap[typeof(DateTime?)] = DbType.DateTime;
        typeMap[typeof(DateTimeOffset?)] = DbType.DateTimeOffset;

To:

        typeMap[typeof(DateTime?)] = DbType.DateTime2;
        typeMap[typeof(DateTimeOffset?)] = DbType.DateTimeOffset;

There's a much easier solution now in a similar question:

SqlMapper.AddTypeMap(typeof(DateTime), System.Data.DbType.DateTime2);

This must be applied before INSERT's. Thanks, @Igand.