Be able to execute two update commands in one transaction using custom queries

[ecerichter]

I would like to be able to execute two update commands (separted by semicolon) in one transaction by using custom queries.
For instance,

begin;
update bankaccount set balance = balance + 100;
update cashaccount set balance = balance - 100;
commit;

I've tried, but I'm always getting an error caused by prepared statements...
Would be possible to completly disable prepared statements? Would Prestd be able to (or need to) understand I do have two commands?