Earning 6k will price me out of singles BTO, then resale too expensive and condo even more expensive. Is there any "hack" to qualify for singles BTO?

There are a few ways.

1) may be to go for Resale flats if you need a house to stay in.
2) Condo If you can afford it, or wants to invest together with it.

3) Not that I want to teach you, but ask your company (if you can) to convert payment as vouchers instead if you are very near the 6k income.

I had the same dilemma as you - but eventually got a freehold condo for investment purposes.
I definitely would not purposely quit my job just to buy property though!