Stumbled across this looking for something else - but can offer some insight that may help others in the future.
You can use the Dapper.DynamicParameters object to add items that can be legally passed to Dapper Queries, i.e. (hand-coded)
var args = new DynamicParameters(new {});
parameters.ForEach(p => args.Add(p.ParameterName, p.Value));
conn.Query<TModel>(sql, args );
HTH