networking - Change DHCP lease time on VirtualBox -

my company using virtualbox+hostmanager our vagrant provider. have plenty of different projects each gets own setup attached ended meta-project of sorts contains vagrant stuff:

• projecta/
• projectb/
• projectc/

inside each project have layout like:

projecta/      puppet/     src/        # project's source, not part of meta-project, auto-created     puppetfile     vagrantfile 

src/ gets created vagrant provisioning , checked out each own vcs project. so, if working on projectb, go folder, vagrant up (which starts or creates required machine, checks out source if needed, sets www.projectb.dev hosts entry on machine , you're go), work on , vagrant halt or vagrant destroy. works well.

the problem virtualbox's dhcp server (which provides dynamic ip address each box) gives out short lease (like, day or two). not every project being worked daily, machines aren't renew lease , end /etc/hosts like:

172.28.128.4    projecta # used 172.28.128.3    projectb 172.28.128.5    projectc 172.28.128.4    projectd # reused :( 

this not ideal situation becomes unmanageable after while, non-networking-savy frontend guys.

so, there way around this, either changing lease time on virtualbox dhcp server or client (the base box custom centos 6 build)? go static ip route per project, opens can of worms, i'm looking @ last resort.