option with different price (not adding)

Hello

First of all, your plugin is perfect and very simple to use 😉
This is my scenario:

I sell web hosting and i want to add ANNUAL option in the product page.
For example : monthly $30, annual : $300
I´ve already set your plugin here, ADDING $270 in the above case.

MONTHLY : $30
ANNUAL : +$270
Then it shows : $300

Is any way to NOT add the difference but put $300 and when the user choose the annual option the product value change from $30 x $300 ?

I hope to explain mysefl well 😉
Thanks
Fabian

The page I need help with: [log in to see the link]