Copy activity dynamic mapping

Hi,

we have a data pipleine with  copy activity, we read data from SAP DSP and write to a lakehouse table. 

some of the SAP fields are TimeSPan which are not supported by lakehouse, so we enable explicity mapping and change the type to string. This works fine. 

Now we want to go a step further, and work towards creating a pipeline that dynamically constructs the json mapping - conforming to the source and sink tags that you see with the explicit mapping.

we read the source column types and if it timespan, we create ssink as physicalType: string. 

this dynamically consttructed json mapping is then passed to the copy activity. 

However, this doesn't work, the mapping doesn't get applied.  So wanted to check with the team here if they have done or faced some similar and if there is way to address this. 

thanks