At work, that's where I was!!
What you need is one of these babies from a Jag - but as the page shows that they have a tendency to melt, wire the contacts of this latching relay so that they only switch your existing high/low beam relay(s).
http://jag-lovers.org/lumps/tech/basics/relays2b.htm
Note though, the author has got the relay type as DPDT, which it's not - it's SPDT!
Simply connect the coil of this latching relay through your momentary-type push button on the stalk!
Simon.