Poor DV Performance with UNION and Columns of different datatypes

Issue

• In my Teiid project, I have two data sources, A and B. Both are Oracle databases.
  Datasource A contains table T of the following structure:

  ID number
  VALUE varchar2

Datasource B contains very similar table T. The only difference is "ID" field data type:

ID  varchar2
VALUE varchar2

T.ID field is indexed in both databases.

Now, I use Teiid to virtualize A and B data sources. I have separate model for each data source and a common model used by end users. Common model contains virtual table T defined as:

select convert(id, string) as ID, VALUE, 'A' as DATA_SOURCE from A_MODEL.T
union all
select ID, VALUE, 'B' as DATA_SOURCE from  B_MODEL.T

Now, the issue comes when user executes query like this:

select * from COMMON_MODEL.T where DATA_SOURCE='A' and ID in ('1', '2')
which is translated by Teiid into the following source query:
select * from A_MODEL.T where convert(ID,string) in ('1','2')
which is translated into the following Oracle query:
select * from T where to_char(id) in ('1','2')

"to_char(id) in ('1','2')" predicate does not allow Oracle to use index built on ID field, so query performance is poor. How can I workaround this?