To open two accounts(usernames) (or more) for yourself then you have to have different ways of funding them ie different switch cards (Ie different bank accounts).
Strongly recommend that you dont use a credit card to fund it. I started one up with £200 from a credit card...now everytime I want to with draw from it, I have to call the BF help desk and wire it to my bank (apparently you cant withdraw to a credit card..it was either that or the fact that I was trying to withdraw more than I had initially paid in?, either way a pain). I have just started using that money in that account to hedge some of my football trading...so if anything I expect that account to drecrease slightly over time, so not too worried.
If you do setup more than one account that will be trading from your home (ie using the same IP address)..then what I did for my daughters account was have it verified..see:-http://help.betfair.com/contents/itemId ... ex.en.html
..That way they could see she was totally independant from me. You need to do this or they will link and associate the two accounts.
I think the other thing that is a bit of a no no is say using your wife account to lay a selection and then you back it (a away of getting around the premium charge)..they will very quickly pick this up. So just be careful...
Thanks and good luck!
PS..stating the obvious..but if you do have more than one account in YOUR name...you will still be bound by the 20 req / sec..!