SQL & PL/SQL :: How To Use VArray In Using Clause Of Execute Immediate

I'm trying to optimize an application running heavy updates/inserts/deletes, by having it using bind variables instead of "string queries".

The columns to be updated can vary (possibly from one column to all columns of a table), thus I have made som logic to build the query accordingly. My problem is now that I cant get the EXECUTE below to handle the VARRAY passed in the USING clause, it fails with "PLS-00457: expressions have to be of SQL types"

Environment:

create table table_x (a varchar2(10),b varchar2(10),c varchar2(10),d varchar2(10));

insert into table_x values('a','b','c','d');
commit;

Code, simplified with static number of columns:

declare
type v is varray(10) of varchar2(20);
v_values v:=v('A','B','c');
myupdate varchar2(2000);
begin
myupdate:='update table_x set a=:a, b=:b where c=:c';
dbms_output.put_line(myupdate);
execute immediate myupdate using v_values;
end;

I've understood that I cannot send TABLE type variables by USING, but this should be an VARRAY.