Im not really sure what you can do. We had the point and fine system to, but i think what kinda of helped was that our events were classed.
Our colors are red, buff (delicate shade of yellow, pinkish-yellow)), and green. So we had....

Red Events- Mandatory (such as intiation, house association meeting, chapter.)
Buff Events- Had to attend like 50% of them (new member ceremonies and events, etc)
Green Events- attend like 20% (Greek Week, movie nights, etc). Plus you always had to give and excuse note for why you couldnt attend an event at least a week in advance.

I think that kind of made it easier for us, we didnt feel like we had to attend everything and scramble around trying to get out of work, study groups, or previously planned stuff.
We just promoted our events and made them out to be fun and helpful to our sisterhood and gaining more girls.