Morning pb,
If you are talking about the designing your site via InstantPro, then there is no way to do what you are asking. It is currently not possible (nor will it be in future as far as I am aware) to access this service without being logged into the holding MyFreeola account (i.e. yours). This means, if you were to use IP, you would have to do all the work or giving your mate access to your account.
If you are going down the VIP/standard hosting route all you would need to give your mate is the FTP information (found within your MyFreeola account) this, assuming the site is signed up for VIP or he is on a Freeola 'net connection, will allow him to upload files to this webspace and this webspace alone without the potential of him compromising other aspects of your Freeola account.
Thirdly, as Neil pointed out previously, you can use a CMS which would allow anybody with the set username and password access to the software enabling them to make changes or additions to the site. Obviously this will be limited to what the CMS can do in terms of design and editing functions. The initial files will also need to be uploaded by you on your Freeola internet connection if you were not looking to sign up to VIP Hosting.
Myself and a couple of others in the office have provided guides to some of the more popular CMS/Blogging softwares in the Help and Support section of the Freeola site. If you are looking to go down this road I would advise
giving them a read (third section down).