Load balancing, persistence and HEAD request

i've setup two VIPs to make HTTP/HTTPS LB with a pool composed by two members. The default persisten profile is "cookie" method with 1H expiration. When the first connection is established, all the othere request continue to go on the selected member. The problem occurs when we get and HEAD request. We use an external site that polling our webserver to check the availability of services, this site use and HEAD request and not a GET request, so the lenght of contect is alwasy 0. There is this SOL http://support.f5.com/kb/en-us/solutions/public/13000/500/sol13521.html that seems to descrive my issue, when this external site send an HEAD request, the first one (that is a login) goes to one member1, the other one (another HEAD request for 200 OK) to the member2 and this isn't right way. Sometime the request goes well, each two with relative response goes only the first member, but most of the time one the problem is what I described above

How I can solve this issue?

This mechanism doesn't use a cookie for pesistence :(

thanks!