sending delay between batches

Hi, I'm using mass contact a lot and enjoy the features of this module. On 1 site I have 250 members to mail and there's a bump into a problem with the mailhost. I split up my mails in packs of 50 because limit no 1 is max 100 adresses per mail. Here I have no problem.
The second limit is max 150 mails (email adresses) per minuut. Since the module is so fast I can only reach 150 of the 250 persons.

So, Is it possble to add a delay in sending between each batch for example 30 seconds?

Anybody wants to write a patch?
I would be very greatfull