Make a query to contain your SQL.
Set the report RecordSource to that query.

In code:
  Build your sql string.
  Change the query's' SQL property to that.
Example:
  stSql = stSql & strWhereClause & ";"
  CurrentDb().QueryDefs("myQuery").Sql = stSql

Voila. You report will use what you built in "stSql" from now on.
This seems like a good way to do this (I am a newcomer to Access.)