Reserve money with Paypal

[rtacconi]

Hi,

I am developing a kind of group by application. I need to do the
following with paypal:

1. Some users accept a group by deal (costing 10$ per user)
2. For each users accepting the deal I reserve 10$ with paypal
3. The minimum item requirement is met
4. The users are charged 10$

If the minimum quantity number is not met:

1. Some users accept a group by deal (costing 10$ per user)
2. For each users accepting the deal I reserve 10$ with paypal
3. The minimum item requirement is not met
4. The users are not charged and I release the money reservation (10$
per each user).

Question is:

Can I reserve x amount of money with paypal? Can I charge later the
user for the amount I reserved before? Can I release the money I
reserved if the group by does not met the requirements?

I know it is a more Paypal question, but I would like to know if
ActiveMerchant can do that and if it is not possible with paypal which
company do that?

Thanks in advance